UPDATE (2024-08-24) : I have updated these house rules... See my 2024 Updated rules post in the discussion thread below.

Though I'd share my house rules with the community. 

Note: I don't use all these house rules for every campaign or every group I play with. I adapt the number of rules to each table. I also don't expect the players to know all these  rules by heart. I have created a "magic item" that lists the rules; the players can add the item to their inventory and read them whenever they want. I try to integrate the rules progressively. Heck, I sometimes forget some of them myself during play!

I've been playing D&D since 86 (1st edition), so there are what some might consider some "grognard" rules in the list. :P

25 House Rules

1. Ability Scores

Use standard array or point buy.

You get a racial feat appropriate to your lineage if you used point-buy or the standard array for your ability scores, and are willing to lower a score by 2.

If using the One D&D playtest rules, you get a Level 1 feat from your background. You can choose a Level 1 racial feat instead. Level of feats that aren't part of the playtest is determined by the DM.

If you create a character for a one shot adventure that last only a couple of sessions, you can choose to roll dice in the character builder, choosing among 3 different sets of 6 x 4d6, drop lowest die method. If that character is later used for a long term campaign or adventure, the DM might ask to set back your default scores using point buy.

Bear in mind House Rule 3 when determining Strength score.

 

2. Variant Encumbrance - aka Strength not an automatic dump stat

In the Character Preferences, choose "variant encumbrance" from the drop down menu, but toggle ON Ignore Coin Weight. 

Normal, "easy" encumbrance rules are to make life easier when using pen & paper, so players don't have to worry about calculating weight and risking bogging the game down. But D&D Beyond calculates everything for you, so there's no reason not be somewhat realistic when it comes to carrying stuff and wearing heavy armor...

3. Multiclassing

Multiclassing is an optional rule in 5E. Any multiclassing must make sense from a roleplaying perspective (i.e. fit the character's personality, take into account its background, and follow the current story narrative). Feats can be used to diversify a character's abilities rather than multiclassing. A number of interesting homebrew feats are available to increase characterization options.

Some multiclassing options open the door to play complexity, combos with rule particularities, or shenanigans that can unbalance or bog down the game. If you do multiclass, you must meet the necessary prerequisites and follow these house rules :

• Dual-class only (no more than 2 classes).
• No 1 level dips. You must invest in gaining at least 2 or 3 levels in your secondary class before you reach character level 10 (or at least 2 consecutive levels after level 10). 
• No paladin/other spellcasting class or warlock/other spellcasting class. Would be wizard/clerics (theurgists) are encouraged to play a wizard of the (improved) War Magic tradition, or a cleric of the (improved) Arcana domain.

That being said, there might be a good story reason for an exception to any of these multiclassing house rules. In which case, you are encouraged to discuss your character ideas with the DM.

Thematically speaking, limiting the warlock normally makes sense, since the warlock is a character that makes a pact with a dangerous or mysterious entity to gain magic powers. Why would a creature make such a pact if it felt it was able to achieve similar powers through study, manipulating natural energies, or the devout worship of a deity? However, there can always be exceptions that fit the narrative.

 

4. Alignment and Background

Player characters are expected to be the "heroes" and the "good guys". If you want to play an "evil" character, keep these guidelines in mind:

• Your character must have a motivation other than naked greed, lust for power, or just being a murder hobo. It must be capable of working with the party without betraying them at every opportunity.
• Your character must not consciously think of themselves as a "bad guy" or "villain". It does not do anything simply "because he's evil." Even evil characters understand and exercise restraint. Followers of evil deities in a well-ruled land or city worship largely behind close doors.

5. (Relatively) Low-Magic Campaign

In small urban areas, magic abilities are feared or frowned upon. Creatures with arcane spellcasting abilities are uncommon, and high-level spellcasters are very rare. Larger urban areas like Waterdeep, Mulmaster or Calimport may have more creatures with magic abilities (and common magic items), but there are laws that regulate magic use in public. In certain areas, public spellcasting might attract the attention of witch/warlock hunters and religious inquisitors.

Characters with divine spellcasting abilities (i.e. clerics, paladins) are very rare. Most priests, monks, and clerics of religious orders and associations have no divine powers. For this reason, divine spellcasters are often admired by the common folk but shun by envious or fearful coreligionists. When roleplaying your character, try to think about their sense of awe and wonderment when they discover their magical abilities -- or when witnessing the magical abilities of their allies for the first time. 

To help you define your background and backstory, see This is Your Life in Xanathar's Guide to Everything. 

6. Average Hit Points

You don't roll for hit points when gaining a level. In Character Preferences, choose "Hit Point Type : Fixed". If you really want to roll the die, set the option to "Manual", and you must roll in front of the DM. If you roll a 1, it becomes a 2. 

7. Languages

In the Forgotten Realms, the Common tongue is divided in four main dialects : Chondathan (Sword Coast, Cormyr, Sembia, northern Faerun), Alzhedo (Calimshan, southern Faerûn), Shou (Kara-Tur), and Chultan (jungles of Chult, Maztica). Nomadic tribes such as the Reghed or the Uthgardt also have their own language. 

I assume you speak Common: Chondathan, unless you specify otherwise because of your backstory. On the digital character sheet, you can customize (add) a language.

My improved Linguist feat is a cool way to know more languages.

Linguist (Improved)

You have studied languages and codes, gaining the following benefits:

• Increase your Intelligence score by 1, to a maximum of 20.
• You learn three languages of your choice. 
• You know the comprehend languages spell, which you can cast as a ritual or using spell slots you have of the appropriate level.
• You can pick up the basics of a conversation carried on in a foreign language. Make a DC 15 Intelligence check (DC 20 for exotic languages). On a success, you have a general sense of what the creature is talking about and you can communicate basic ideas. The higher your check result, the more you understand what a creature is trying to communicate. 
• You can add your proficiency bonus to Wisdom saving throws against spells that target you that include spoken words or instructions, such as vicious mockery, command, geas, or suggestion. 
• You can ably create written ciphers. Others can't decipher a code you create unless you teach them, they succeed on an Intelligence check (DC equal to your Intelligence score + your proficiency bonus), or they use magic to decipher it.

8. Improved / Revised Subclasses, Feats, Spells, etc. 

The game has evolved over the years, and knowledgeable members of the D&D community voice their opinions about which class or subclass is weaker or stronger, and which features, feats, or spells should be improved, revised, or added. I'm always looking for ways to improve the game based on feedback and analysis from these nerdy DMs and players in D&D forums, articles, and podcasts. If a feat or spell is generally considered weak, poor, or lackluster by the community, I will try to improve it. If it is generally considered overly powerful or "broken", I will try to balance it while maintaining its usefulness. In effect, we are playing a homebrew version of D&D 5.5. A "revised" version of a spell often includes Rule As Intended ruling (Sage Advice) by lead rule designer Jeremy Crawford, or is revised for game balance.  

After creating your character, open your digital character sheet and go to Feats > Manage Feats > and choose the Improved Class Features feat relevant to your chosen class. This "feat" will give you additional or variant features, and tell you which Optional Features (from Tasha's Cauldron of Everything) you can toggle on in the character builder. 

If you're not sure about any of this, the DM will do it for you :)

8b. Reskinning

As long as you aren't changing the actual mechanics of a class, of a spell, or "how things work", we are lenient in allowing reskinning and reflavoring some abilities and spells.

Example: fire is an easily countered damage type. Most of the elemental types (cold, fire, lightning, and thunder) are very commonly resisted, as is poison, so it’s fine to modify fireball and create a similar spell that uses one of these damage types. However, force, necrotic, psychic, and radiant damage are all dangerous options because few creatures are resistant to them. Talk to your DM for reskinning ideas.

See also Personalizing Spells in Tasha's Cauldron of Everything.

9. The Breather (10-Minute Break)

Introducing the Breather (10-Minute Break). There is no limit to the number of breathers you can take in a day.

• At the end of a breather, you can spend 1 hit die (only one).
• Any amount of combat or strenuous activities interrupt a breather.
• Six breathers in a row amount to a short rest.
• If really pressed for time, the adventuring party can gain the benefit of a short rest in 10 minutes provided the PCs can all spend at least 1 Hit Die. Once they use a breather this way, it can't be done again until the characters complete a long rest.

10. New Conditions

Bloodied

A creature is bloodied when its hit points are equal to or less than one-half of its maximum hit points, rounded down. One-half of its maximum hit points, rounded down, is referred to as its "bloodied value".

• A bloodied creature suffers a temporary level of exhaustion (see exhaustion PHB p. 291). This temporary level of exhaustion is immediately reduced once the creature is no longer bloodied.

During combat, a bloodied creature can use a bonus action to burn Hit Dice (sacrificing two of them), drawing upon inner strength and adrenaline to suppress the bloodied condition until the end of the encounter. If the party is facing a particularly deadly encounter, the DM may adjudicate that the bloodied condition is suppressed for all player characters in a dire situation without spending any Hit Dice, reflecting the survival instinct.   

As an action, someone with proficiency in the Medicine skill can expend one use of a healer's kit to help a creature that is bloodied (including themselves). When they do so, the temporary level of exhaustion caused by the bloodied condition is suppressed for 1 minute (or 10 minutes if the healer is also proficient in the herbalism kit and has it readily available). If the character has the Healer's feat or the Fast Hands rogue feature, it can do this as a bonus action.

Undead, construct, oozes, and legendary creatures are immune to the bloodied condition. 

Bound

• A bound creature can't move or take reactions. The only action it can take is to cast a spell that doesn't require somatic or material components, or attempt to escape the binds with a Strength (Athletics), a Dexterity (Acrobatics), or an Intelligence (Sleight of Hand) check. 
• If the bound creature is also gagged (mouth stopped up to prevent speech), it can't cast a spell that requires a verbal component. 
• The creature automatically fails Strength and Dexterity saving throws.
• Attack rolls against the creature have advantage.
• Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature. (Possible coup de grâce at the DM's option.)

After three failed ability check escape attempts, a creature cannot usually try to escape again until a certain amount of time has elapsed. The DM can adjudicate based on the DC to escape the bonds, the result of the creature's ability checks (degrees of success), or the environment. In a combat situation, a creature can normally attempt to escape bounds once per turn, emboldened by a sudden adrenaline rush.

Surprised 

• A surprised creature can't move or take an action on its first turn of the combat.
• An attacker has advantage on its first attack roll if it attacks from a hiding position, or moves within reach of the surprised creature without being seen. 
• The creature can't take a reaction until the end of its first turn.
• At the end of its first turn, the surprised condition ends. 

The DM determines who might be surprised. If neither side tries to be stealthy, they usually notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side (-5 to the passive score in dim light). Any character or monster that doesn't notice a threat is surprised at the start of the encounter. A member of a group can be surprised even if the other members aren't. When an unseen attacker makes an attack, it gives away its location whether the attack hits or misses (PHB ch.9 : "Unseen Attackers and Targets").

If the two sides are suspicious of one another, such as in a tense stand-off, they are considered ready for combat. They might be "surprised" by an opponent's sudden move or action, but they won't get the surprised condition.

Staggered

• A staggered creature's speed is halved
• The creature has -2 AC and -2 Dexterity saving throws
• The creature can't use reactions, and it can use either an action or a bonus action on its turn, not both.
• The condition ends at the end of the creature's next turn.

11. Dropping to 0 Hit Points

To avoid metagaming, death saving throws are rolled secretly by the DM.

When regaining hit points after falling to 0 hit points, you suffer the staggered condition (see rule # 11). 

12. Familiars

• A familiar can't normally help you with "knowledge" ability checks (Arcana, History, Nature, Religion). See house rule 18b.
• A familiar can attune to one magic item if its Intelligence score is 6 or higher.
• A familiar can't make a creature drink a healing potion (or other potion) during combat unless it has opposable thumbs (e.g. monkey).
• The augment familiar spell includes new benefits for your familiar. Check it out!

13. Spell Focus

Divine casters with shields (clerics, paladins) are assumed to use a shield emblazoned with their holy symbol or sacred oath symbol as divine focus. They can perform the somatic components of spells even when they are wielding a weapon and a shield. (HR) To use a simple or martial weapon as a spellcasting focus, a spellcaster can also shop around for a ruby of the war mage (50 gp). Sorcerers can eschew material components (don't need them), unless a material component's value is over 100 gp. See Improved Sorcerer Features "feat" for details.

14. Healer's Kit & Medicine Proficiency

If you have proficiency in the Medicine skill, you gain extra benefits when using a healer’s kit. The Healer feat has also been improved.

Healer (Improved)

You are an able physician, blessed by the gods of life, allowing you to mend wounds quickly and get your allies back in the fight. You gain the following benefits:

• You gain proficiency in the medicine skill if you don't have it already.
• When you use an action and spend one use of a healer's kit during combat, a target that isn't unconscious may immediately spend 1 Hit Die.
• Once per day, after a short or long rest, you may expend one use of a healer's kit to grant a creature a new saving throw against one disease or one condition. That condition must be blinded, deafened, paralyzed, or poisoned. If the effect that created the condition had no saving throw, the save DC is 20. 
• You can cast cure wounds at its lowest level. Once you cast it, you must finish a short rest before you can cast it again using this feat. 

15.  Identifying an Item / Attunement

Proficiency with the Arcana, Nature or Religion skill (depending on the item; usually Arcana)-- or the identify spell, is required to learn a magical item's properties and the way to use it during a short rest. 

Becoming attuned to an item requires 10 minutes (instead of 1 hour), which can be done during the same short rest you use to identify the item. Without becoming attuned to an item that requires attunement, a creature gains only its nonmagical benefits, unless its description states otherwise. If a character dies, even for less than 1 minute, attunement to a magic item is instantly broken. As RAW, you can voluntarily end attunement by spending another short rest focused on the item, unless the item is cursed. A creature's attunement to an item also ends if the creature no longer satisfies the prerequisites for attunement, if the item has been more than 100 feet away for at least 24 hours, if the creature dies, or if another creature attunes to the item. 

16. Monster Knowledge

There is player knowledge and character knowledge. With regards to monstrous creatures, characters know about the tales and legends of popular creatures such as lycanthropes, vampires, trolls, and zombies, but might not know about specific abilities, vulnerabilities or immunities.

Passive Intelligence scores (Arcana, History, Nature, or Religion) will be used by the DM to determine character knowledge about a specific creature. During combat, you must spend an action to roll a relevant check and try to beat your passive score. 

17. Object Interactions

On your turn, you can interact with two objects or features of the environment for free, during either your move or your action (RAW = one object interaction). Example, on your turn: you can draw two swords instead of just one. You can draw one sword and kick open a door. You can drink your ale and grab your knife on the table. Whatever makes sense in a 6 seconds round.

Potions are assumed to be readily available during combat, stored using a potion belt or other accessible pockets. However, the DM might require you to use an action for any activities when it needs special care or when it presents an unusual obstacle. For instance, the DM could reasonably expect you to use an action to open a stuck door, turn a crank to lower a drawbridge, or unsling your backpack, open it, and retrieve an object.

You can use a bonus action to quaff a potion of healing. Administering a potion of healing to another character still takes an action, as does drinking any other magic potions. This is a game balance thing, as many potions are bottled spells that momentarily "daze" the drinker upon consumption.

18. Resistance and Immunity to nonmagical bludgeoning, piercing, or slashing damage

• The common magic weapons introduced in Xanathar's Guide to Everything (e.g. a moon-touched sword) or those that have only minor magical properties (such as a dagger that never gets dirty) do not overcome resistance or immunity to nonmagical bludgeoning, piercing, or slashing damage. The weapon must grant a bonus to attack and damage rolls, or be at least uncommon in its rarity. 
• If a monster's stat blocks states the creature is immune or resistant to bludgeoning, piercing or slashing damage from "nonmagical attacks", it will be treated as immune or resistant to "nonmagical damage" from these damage types (which can potentially include damage from failed saving throws, such the one required by a scything blade trap). 
• A creature immune to nonmagical bludgeoning damage takes half damage from a fall (as if resistant to bludgeoning damage, not immune).

19. Skill Checks

Simply describe your character's actions. The DM will ask if a skill check -- if any-- is required for a given situation. Never roll in anticipation, because it slows the game down, and a skill's passive score might be enough while a low number on the die will always count as a failure. Some actions might require proficiency in a given skill, tool, or instrument (DM's call).

Your character's Passive Perception score is used for general detection of "things that are out there" including monsters and traps. No need to specify you are using your perception skill unless you are trying to beat your passive score. Reminder: there's a -5 penalty on your Passive Perception score when your are in a lightly obscured or in dim light (darkness for creatures with darkvision). A skill's passive score may also be used by the DM if you try to do something repeatedly : e.g. open a stuck door, pick a lock, look for secret doors.

Rule of thumb: if you don't succeed at first, you can try again (if possible with someone's help to give advantage on the roll). After two attempts, passive scores are used.

19b. Helping Another Character 

• A player has to announce its character is trying to help another one before the relevant ability check is rolled. (Same for guidance spell)
• A character can only provide help if it has proficiency in the skill or tool related to the task at hand, or a relevant ability score equal or higher than the character doing the task. Example: a bard with Arcana proficiency can help a wizard decipher magic runes (advantage on the Intelligence (Arcana) check), but a rogue with a Strength score of 8 cannot help a barbarian with a Strength score of 18 force open a stuck door. 

20. Swimming

You need to be proficient in Athletics to know how to swim efficiently; without proficiency, you can "float" and swim (dog paddle) 5 feet per round in calm water on a successful DC 10 Strength check. (DC 15 in agitated waters). If the Armor table shows "Disadvantage" in the Stealth column, the wearer has disadvantage on Strength (Athletics) checks made to swim. (Exception: padded armor).

21. Athletics / Perception Skills

As written, only a handful of creatures have the Athletics and Perception skills. That’s great for simplicity, but weak for game balance. For the purpose of the grappling and pushing/shoving rules, many fighting type creatures (e.g. orcs, hobgoblins, giants) will be considered proficient in the Athletics skill (DM's call). Creatures and NPCs that have "guarding" duties might get an ad hoc Perception skill proficiency, or even the Alert or Observant feat. 

21b. Escaping a (nonmagical) Grapple

It normally takes an action (Athletics or Acrobatics check) to escape a grapple. If you have the Extra Attack feature (or Multiattack action in the case of monsters and NPCs), you can take the Attack action and replace one of your attacks to attempt to break out of the grapple (instead of using your full action to do so). This doesn't apply if you are also restrained or if you are grappled by a magical effect (such as the entangle spell or Bigby's grasping hand). Using the One D&D playtest rule, the DM might allow a DEX or STR save at the end of a creature's turn to break a grapple.

22. Lingering Injuries by Damage Type

We use my Lingering Injuries by Damage Type document on the DMs Guild. There is a roll on the relevant lingering injuries table in the following situations:

• Scoring a critical hit (natural 20)
• Failing a saving throw with a natural 1
• Whenever a creature drops to 0 hit points as a result of damage. 

23. Tool Proficiency

If you are proficient in a set of tools, make sure you add to your equipment the tool kit that includes the gp cost in the title; example Cartographer's Tools (15 p). This revised version that I created using the D&D Beyond magic item builder includes optional rules from Xanathar's Guide to Everything on how to use them. 

24. Milestone/ Story-Based Level Advancement

The DM tells you when you go up a level. Might require a long rest and some downtime (training).  

25. On Your Turn in combat...

• On your turn, not much time for lengthy "in character" discussions or strategic talk (since the whole round lasts 6 seconds!) Only "brief utterances" are allowed (PHB p. 189).
• Be ready on your turn. Know your class features and spells. If you don't know what to do, the DM will give you about 20 seconds. If you don't act fast, you will Dodge as an action and finish your turn.
• When playing online, to speed up the game, you can preroll your attacks and note any damage. When your turn comes up, describe what happens based on your roll results. 

Really great list.
Whilst not every one of these suits my games, I like a lot of them and will be using some in my own games.

Same. Really good job. Keep up the good work

 

Here's a Revised version following the 2024 rules change. 

 

Quote from LazerScythe >>

Really great list.
Whilst not every one of these suits my games, I like a lot of them and will be using some in my own games.

 I'm quite late to see your reply, but I hope some of the rules you've adapted from mine have been useful and enjoyed at your table.

I will use that evil rule. I prefer to only have my evil characters be "evil" against one specific faction, but those morals should not contradict anyone else's in the party.

Yeah these are all really awesome, will definetly be using some of these, although Im not the DM for your players but, does rules 25 for 5e really... work out?

Here's a new update on my houseruled / homebrew Conditions and Hazards:

(For my players, I create a special "magic item" called Conditions that they can add to their inventory for quick reference during a session). 

Homebrew conditions and hazards, and changes to official conditions, are marked with the ᴮᴹ tag.

ALERT [CONDITION] ᴮᴹ

While you have the Alert condition, you experience the following effects.
Attentive to surroundings. You have Advantage on Wisdom (Perception) checks, and your Passive Perception score increases by +5.
Ready for combat. When you roll Initiative, you can add your Proficiency Bonus to the roll, unless you are Surprised. This does not stack with the bonus from the Alert feat.
Ending the condition. The Alert condition ends if you become Distracted, Incapacitated, Intoxicated, or Unconscious.

Standing Watch. When you begin a guard shift while camping or resting, you must make a DC 10 Constitution saving throw. On a success, you gain the Alert condition for that shift. On a failure, you are too tired or distracted and can’t benefit from the condition. You may swap with a companion who can stand guard.

You can assume the Alert condition while actively keeping watch, standing guard, or otherwise focusing on possible threats in a fixed location. Creatures assigned to guard a location are typically Alert at the DM’s discretion. You can't benefit from this condition if you have more than 1 Exhaustion level.

BEWILDERED [CONDITION] ᴰᴿ

You can’t cast spells, except for cantrips with a casting time of 1 action.

BLINDED [CONDITION] ᴿᴬᵂ

While you have the Blinded condition, you experience the following effects.
Can't See. You can't see and automatically fail any ability check that requires sight.
Attacks Affected. Attack rolls against you have Advantage, and your attack rolls have Disadvantage.

ᴮᴹ The DM can impose Disadvantage on a saving throw against a visible effect when it makes narrative sense, such as a Dexterity saving throw against a Lightning Bolt zap.

BLOODIED [CONDITION] ᴮᴹ

A creature is Bloodied when its hit points are equal to or less than half its maximum hit points (rounded down).

While you have the Bloodied condition, you experience the following effects.
Wounded. You gain 1 Exhaustion level. This Exhaustion is temporary and immediately ends when you are no longer Bloodied.
Blood Rush. While you are in combat, you suppress the effects of the Exhaustion gained from this condition. In addition, you have a +1 bonus to melee attack rolls and Strength saving throws.
Adjudication. The DM can decide that certain creatures aren’t affected by the Bloodied condition or show no visible signs of damage. Other expressions may be used for flavor: Constructs and Undead are Battered, Oozes are Jellied, Plants are Wilted, and Elementals may be Fractured or Dispersed.

BOUND [CONDITION] ᴮᴹ 

While you are Bound, you are Paralyzed, with the following exceptions.
Limited Action. You can take an action to cast a spell that doesn't require Somatic or Material components, or attempt to escape the binds with a Strength (Athletics), a Dexterity (Acrobatics), or an Intelligence (Sleight of Hand) check. 
No Speaking. If you are gagged or otherwise prevented from speech, you can't cast a spell that requires a Verbal component. 

After three failed ability check escape attempts, you cannot usually try to escape again until a certain amount of time has elapsed. The DM can adjudicate based on the DC to escape the bonds, the result of the creature's ability checks (degrees of success), or the environment. During combat, you can normally attempt to escape bounds as an action on each of your turns, emboldened by a sudden adrenaline rush.

BURNING [HAZARD] ᴮᴹ 

Ongoing Damage. A burning creature or object takes Fire damage at the start of each of its turns. The damage scales with the creature’s level or Challenge Rating: 1d6 (level or CR 1–4), 2d6 (5–10), 3d6 (11–16), or 4d6 (17+).
Self-Extinguish. As an action, you can extinguish the flames on yourself by falling Prone and rolling on the ground.
Environmental Extinguish. The flames go out if the burning creature or object is douzed, submerged, or deprived of oxygen.
Aid. You or another creature can use the Utilize action to empty a full waterskin (4 pints) onto the flames. A waterskin is considered full if it has not been used since your last Short Rest or if you specifically refilled it.

BURIED [HAZARD] ᴮᴹ 

While you are Buried, you experience the following effects.
Sight and Mobility Affected. You have the Blinded, Prone, and Restrained conditions.
Possible Suffocation. You must make a DC 13 Constitution saving throw. On a successful save, you have a lungful of air and can hold your breath for a number of minutes equal to 1 + your Constitution modifier (minimum 30 seconds) before suffocation begins. On a failed save, you can only hold your breath a number of rounds equal to your Constitution modifier (minimum of 1 round). When you run out of breath, you gain 1 Exhaustion level at the end of each of your turns. If you reach 6 Exhaustion levels, you fall to 0 Hit Points and start making Death Saving Throws (instead of dying outright).
Escape. As an action, you can make a Strength (Athletics) check to attempt to escape. A creature that isn't Buried can also use their action to make the check or assist you with the Help action. The DC equals 15 or the DC of the spell or effect that caused the condition. If you are freed and can breathe again, you remove all levels of Exhaustion you gained from suffocating, unless a spell or effect tells you otherwise. 

CHARMED [CONDITION] ᴿᴬᵂ

While you have the Charmed condition, you experience the following effects.
Can't Harm the Charmer. You can't attack the charmer or target the charmer with harmful abilities or magical effects.
Social Advantage. The charmer has Advantage on any ability check to interact socially with you.

Charm effects from specific monsters and spells may have additional benefits, as specified in the stats block or spell description. For example, a vampire might be able to force a Charmed target to attack an ally.

If another creature charms a Charmed creature with the same spell or effect, only the most powerful charm effect applies while the durations overlap (XGTE). This will be determined by comparing the spell slots used to cast the spells, or by the save DCs if spells were cast at the same level or if the charm effect doesn't have a spell level. If both "charms" are of equal strength, the most recent one takes effect while the durations overlap. 

CONCENTRATION

Some spells and other effects require Concentration to remain active, as specified in their descriptions. If the effect’s creator loses Concentration, the effect ends. If the effect has a maximum duration, the effect’s description specifies how long the creator can concentrate on it: up to 1 minute, 1 hour, or some other duration. The creator can end Concentration at any time (no action required). The following factors break Concentration.

Another Concentration Effect. You lose Concentration on an effect the moment you start casting a spell that requires Concentration or activate another effect that requires Concentration, unless the spell or effect has the (homebrew) Dual Concentration feature specified in its description.
Damage. If you take damage, you must succeed on a Constitution saving throw to maintain Concentration. The DC equals 10 or half the damage taken (round down), whichever number is higher, up to a maximum DC of 30.
ᴮᴹ Dazed. If you are Dazed by a spell or effect but take no damage, you must succeed on a DC 5 Constitution save to maintain Concentration. A natural 1 on this save is an automatic failure.  
ᴮᴹ Environmental Disturbance. The DM can decide that some environmental phenomena, such as a violent earthquake or a wave crashing over you while you’re on a storm-tossed ship, requires you to succeed on a DC 10 Constitution saving throw to maintain Concentration, even if you take no damage. 
Incapacitated or Dead. Your Concentration ends if you have the Incapacitated condition or you die.

CONTAMINATION [CONDITION] ᴰᴿ 

Characters in the world of Drakkenheim may be exposed to eldritch pollutants or arcane radiation emitted by delerium. These hazards cause a new condition called Contamination, which causes otherworldly Mutations that have both detrimental and beneficial effects. At the DM's option, other effects outside the world of Drakkenheim might impose Contamination. 

See * Contamination "magic item" for details.

CORRODING [HAZARD] ᴮᴹ 

If a spell or effect specifies ongoing acid damage or a corroding hazard, that description takes precedence over this hazard.

Simple Contact. A creature that touches acid takes 5 (2d4) Acid damage.
Ingestion. A creature that ingests acid takes 10 (4d4) Acid damage and 10 (4d4) ongoing Acid damage at the start of its next 3 turns, or half the initial damage and no ongoing damage on a successful DC 13 Constitution saving throw.
Moving Into or Ending Turn. A creature that moves into an acid-filled area or ends its turn there takes 10 (4d4) Acid damage.
Submersion. A creature entirely submerged in acid takes 25 (10d4) Acid damage at the start of each of its turns and 10 (4d4) ongoing Acid damage for 3 turns after leaving the acid.
Ending Ongoing Damage. A creature can use an action to wipe away the acid. Magical healing also ends any ongoing damage.
Corrosive Scarring. A creature that takes more than 50 Acid damage from this hazard has its Charisma score* reduced by 2. This reduction lasts until the creature receives a Greater Restoration spell, a Potion of Superior Healing, or a healing spell of 5th level or higher.
Metal Objects. At initiative count 20 (losing ties), each nonmagical metal weapon submerged in acid takes a permanent −1 penalty to damage rolls, and each nonmagical metal armor or shield takes a permanent −1 penalty to AC. A weapon reduced to −5 damage, or armor/shield reduced to AC 10/+0, is destroyed.

* And Allure proficiency drops one level (Expertise → Proficient → Half Proficient → Not Proficient)

CROWDED [HAZARD] ᴮᴹ 

While in a Crowded urban environment, you experience the following effects:

Difficult Terrain. Your movement speed is halved as you navigate through throngs of creatures.
Disrupted Perception. You have Disadvantage on Wisdom (Perception) checks to perceive anything inside or outside the crowd.
Collateral Risk. When you make a ranged attack while Crowded and you roll a 1, 2, or 3 on your attack roll, your attack strikes a member of the crowd. Large area spells or effects such as Fireball requires a successful DC 10 Intelligence (Arcana) check to avoid hitting noncombatants.  
Frightened Commoners. Most commoners become Frightened if combat is instigated in the crowd. A Frightened creature takes the Dash action and moves away from danger by the safest route on each of its turns unless there is nowhere to move, in which case the creature attempts to Hide.
Mob Wrath. If you accidentally kill a crowd member and you are surrounded by creatures that are not easily Frightened (DM fiat), you must succeed on a Charisma (Deception, Intimidation, or Persuasion) check (DC 13 + 2 per additional incident) to calm the crowd. On a failure, the crowd transforms into a Hostile commoner mob that attacks until you are reduced to 0 Hit Points or the mob is Bloodied.

DAZED [CONDITION] ᴮᴹ 

While Dazed, you experience the following effect:

Limited Activity. You can only do one of the following things on your turn: move, use an action, or use a Bonus Action. 
Concentration Challenged. If you are Dazed by a spell or effect, you must succeed on a DC 5 Constitution save to maintain Concentration, whether or not you took damage. A natural 1 on this save is always a failure.  
Ending the Condition. The Lesser Restoration and Greater Restoration spells remove the Dazed condition. At the DM’s discretion, other powers, spells, or effects might also remove the Dazed condition. 
Immunity. A creature immune to the Stunned or Paralyzed condition is also immune to the Dazed condition. 

When a Dazed creature is affected by a spell or effect that gives them an extra action on their turn (like the Haste spell or the fighter’s Action Surge feature), they can still take this extra action, in addition to the movement, action, or Bonus Action allowed by the Dazed condition.

DEAFENED [CONDITION] ᴮᴹ

While you have the Deafened condition, you experience the following effects.
Can't Hear. You have Disadvantage on Wisdom (Perception) checks and automatically fail any ability check that specifically requires hearing. 
ᴮᴹ Thunder Resistance. You have Resistance to Thunder damage.
ᴮᴹ Spellcasting Affected. When you cast a spell with a Verbal component, roll a d20. On a 1–4, the spell fails due to misuttered words. If the spell was cast using a spell slot, that slot is not expended. If you are both Deafened and muted (such as within magical silence), any spell with a Verbal component automatically fails. ᴮᴹ

Thunder damage is mainly concussive, like a shockwave, but being Deafened should still provide protection. As for spells with Verbal components, the chanting of mystic words require a particular combination of sounds, with specific pitch and resonance (2014 PHB). Being Deafened should make it harder to pronounce these sounds. The DM can choose to roll on the Scroll Mishap table if the spellcasting is affected.

DEMON ICHOR [HAZARD]

Demon ichor is what remains behind after a demon dies. It’s a reduction of demonic blood, viscera, and bodily fluids with the consistency and odor of bile.
Flesh Warping. When a creature comes in direct contact with demon ichor, it must make a DC 10 Constitution saving throw. Fiends, oozes, plants, and undead automatically succeed on the saving throw. On a failed save, the creature is magically warped by the ichor, as determined by rolling on the Flesh Warping table. A spell that removes a curse ends all ichor-related warping effects on a creature.
Ichor-Coated Weapons. A creature that takes damage from a weapon coated with demon ichor suffers a flesh-warping transformation if it fails its saving throw. After hitting its target, the weapon is no longer coated with demon ichor.

See Bottled Demon Ichor magic item for the complete Flesh Warping table.

DISTRACTED [CONDITION] ᴮᴹ

You aren't paying close attention to your surroundings. While you are subjected to the Distracted Condition, you experience the following effects.
Attention Affected. You have Disadvantage on Wisdom (Perception) checks, and your Passive Perception score decreases by -5. 
Poor Reflexes. You can't take Reactions.

EXHAUSTION [CONDITION] 

While you are subjected to the Exhaustion Condition, you experience the following effects.
Levels of Exhaustion. This Condition is cumulative. Each time you receive it, you gain 1 Exhaustion level. You die if your Exhaustion level exceeds 5.
d20 Rolls Affected. When you make a d20 Test, you subtract twice your Exhaustion level from the d20 roll. 
Speed Affected. Each Exhaustion level reduces your Speed by 5.
ᴮᴹ Spell DC Affected. You suffer a -2 penalty to your spell save DC (no matter the Exhaustion level).
Ending the Condition. Finishing a Long Rest in a Safe Haven removes 1 Exhaustion level. Some spells, class features, and items also remove Exhaustion levels. When your Exhaustion level reaches 0, the condition ends.

At the DM's option, tier 1 characters (level 1-4) and creatures of Challenge Rating 1 or lower may substract 1 x Exhaustion level to their d20 Tests rather than twice their Exhaustion level ("Easy Variant" Exhaustion 'items' on the digital character sheet).

FASCINATED [CONDITION] ᴮᴹ 

While you are subjected to the Fascinated Condition, you are entranced by a supernatural or spell effect. You experience the following effects.
Entranced. You stand or sit quietly, taking no actions other than to pay attention to the fascinating effect. The spell or effect specifies if you can move.
Attention Affected. You have Disadvantage on Wisdom (Perception) checks. 
Limited Speech. Your speech becomes fragmented and incoherent. You can only speak in brief, vague sentences or phrases, often unrelated to the current situation. Communication is limited to simple words, sounds, or repeated phrases, making it difficult to convey complex thoughts or ideas.
Ending the Trance. The condition ends if you take any damage, or an ally or other creature uses an action to shake you out of your stupor.

FRIGHTENED [CONDITION] ᴿᴬᵂ

While you have the Frightened condition, you experience the following effects.
Ability Checks and Attacks Affected. You have Disadvantage on ability checks and attack rolls while the source of fear is within line of sight. (DM adjudication.)
Can't Approach. You can't willingly move closer to the source of fear.

DMG variant rule:In special circumstances, for example if you fail the saving throw with a natural 1, the DM can subject you to another effect as long as the Frightened condition lasts (d8):

• (1-3) You must take the Dash action on each of your turn and use your movement to get farther away from the source of your fear.
• (4-6) Attack rolls against you have Advantage.
• (7-8) You are also Dazed (i.e. you can do only one of the following on each of its turns: move, take an action, or take a Bonus Action).

A monster is likely to flee if it starts its turn Bloodied and has the Frightened condition. In those circumstances, you can decide the monster flees (Dash or Disengage action to move away), or you can have it make a DC 10 Wisdom saving throw and flee or attempt to parley or surrender on a failed save. (DMG 2024)

GRAPPLING 

A creature can grapple another creature. Characters typically grapple by using an Unarmed Strike. Many monsters have special attacks that allow them to quickly grapple prey. However a grapple is initiated, it follows these rules. 

Grapple (Unarmed Strike). The target must succeed on a Strength or Dexterity saving throw (it chooses which), or it has the Grappled condition. The DC for the saving throw and any escape attempts equals 8 + Strength modifier + Proficiency Bonus. This grapple is possible only if the target is no more than one size larger than you and if you have a hand free to grab it. Successfully grappling a creature gives it the Grappled condition.

One Grapple per Hand. A creature must have a hand free to grapple another creature. Some stat blocks and game effects allow a creature to grapple using a tentacle, a maw, or another body part. Whatever part a grappler uses, it can grapple only one creature at a time with that part, and the grappler can’t use that part to target another creature unless it ends the grapple.

GRAPPLED [CONDITION] ᴿᴬᵂ

While you have the Grappled condition, you experience the following effects. 
Speed 0. Your Speed is 0 and can't increase.
Attacks Affected. You have Disadvantage on attack rolls against any target other than the grappler.
Movable. The grappler can drag or carry you when it moves, but every foot of movement costs 1 extra foot, unless you are Tiny or two or more Sizes smaller than the grappler.

Escaping a Grapple. A Grappled creature can use its action to make a Strength (Athletics) or Dexterity (Acrobatics) check against the grapple’s escape DC, ending the Condition on itself on a success. The Condition also ends if the grappler has the Incapacitated condition or if the distance between the Grappled target and the grappler exceeds the grapple's range. (Some spells and effects can require a different check or saving throw to escape a grapple.)

ᴮᴹ If you have the Extra Attack feature, you can replace one of your attacks when you use your action to escape the grapple, instead of using your full action to do so, unless you are also Restrained. 

HIDE [ACTION] 

With the Hide action, you try to conceal yourself and make yourself silent.

Requirements. You must be Heavily Obscured, or behind Three-Quarters Cover or Total Cover, and out of any enemy’s line of sight. You can’t hide behind a creature only one size larger than you, unless you have a feature that allows it (such as the Halfling’s Naturally Stealthy trait). If you can see a creature, you can usually tell whether it can see you (DM’s discretion).
Finding a Hiding Spot. Unless you’re in an empty room, you may suggest hiding places to the DM. The DM decides whether hiding is possible in the situation.
Stealth Check. Make a Dexterity (Stealth) check. Your result becomes the DC for creatures trying to detect you with Wisdom (Perception) checks. The DM may instead use a creature’s Passive Perception.
Self-Awareness. If your Wisdom score is 12 or higher and your Stealth result is below 15, you realize that your attempt is mediocre at best in the current circumstances.
Check Reroll. If the scene, environment, or situation changes, the DM may call for a new Dexterity (Stealth) check. You must use the new result.
Group Stealth. When the party moves stealthily together, the DM can have everyone roll Stealth and use the group’s average as the DC. For a grittier approach, the DM may instead use the lowest roll.

 

HIDDEN [CONDITION] ᴮᴹ 

Replaces the Invisible condition when hiding.

While Hidden, you are unheard as well as unseen. You experience the following effects:
Surprise. If you are Hidden when you roll Initiative, you have Advantage on the roll.
Concealed. You aren’t affected by any effect that requires its target to be seen unless the effect's creator can somehow see you. Any equipment you are wearing or carrying is also concealed.
ᴮᴹ Rogue Sneak. A Rogue, or a creature with Stealth expertise (double Proficiency), can sneak up to a target from behind or the side without ending the condition, provided the character stays in Dim Light or Darkness and beats the creature's Passive Perception. 
Attacks Affected. Attack Rolls against you have Disadvantage, and your Attack Rolls have Advantage. (Your first attack normally ends the Condition.)

The Condition ends on you immediately after any of the following occurrences: you make a sound louder than a whisper, an enemy finds you, you make an Attack Roll, you cast a Spell with a verbal component, or you are no longer Heavily Obscured or behind any Cover.

In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the DM might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain Advantage on an attack roll before you are seen.

INCAPACITATED [CONDITION] 

While you have the Incapacitated condition, you experience the following effects.
Inactive. You can't take any action, Bonus Action, or Reaction.
No Concentration. Your Concentration is broken.
ᴮᴹ Speechless. You can't speak or use telepathy.
Surprised. If you're Incapacitated when you roll Initiative, you have Disadvantage on the roll.

INVISIBLE [CONDITION] 

While you have the Invisible condition, you experience the following effects:
Concealed. You aren’t affected by any effect that requires its target to be seen unless the effect's creator can somehow see you. If you become Invisible as part of a spell or other magical effect, any equipment you are wearing or carrying when you become invisible is also invisible.
ᴮᴹ Adaptive Illusion. Tiny objects that you pick up become invisible. Nonmagical substances that come in contact with you such as blood or flour become invisible, but can momentarily reveal your current location.
Attacks Affected. Attack rolls against you have Disadvantage, and your attack rolls have Advantage. If a creature can somehow see you, you don't gain this benefit against that creature.
ᴮᴹ Limited Stealth. A creature within 30 feet of you that doesn't have the Deafened condition knows your approximate location and can move to attack you. If you want to make sure you are unheard as well as unseen, you must take the Hide action. 

A creature in melee combat with you can usually determine your approximate location; it might not see you, but you are making noise as you move around, breathing, shuffling, clipping bushes, hitting the cobblestone, stirring up dust, leaving footprints, stepping in a puddle, bumping into furniture, or swinging your weapon.  

The DM can decide that an invisible creature's location is unknown to combatants because of the environment, the combatants' attentiveness, or the distance separating the creature and the other combatants. They might be distracted or simply just not paying attention.

If a creature is Hidden as well as Invisible, the DM can impose Disadvantage on a creature's Wisdom (Perception) check to find its location when taking the Search action, especially if the Invisible creature is more than 30 feet away.

MASSIVE DAMAGE [HAZARD] ᴮᴹ

When you take damage from a single source equal to or greater than half your Hit Point Maximum, you must succeed on a DC 15 Constitution saving throw or suffer a random effect determined by a roll on the System Shock table.

System Shock

d10	Effect
1	You drop to 0 Hit Points and start dying (Death saving throws)
2–3	You drop to 0 Hit Points but you are stable.
4–5	You are Stunned until the end of your next turn.
6–7	You can’t take Reactions and have Disadvantage on d20 Tests until the end of your next turn.
8–10	You gain 1d3 Exhaustion levels.

PARALYZED [CONDITION] ᴿᴬᵂ

While you have the Paralyzed condition, you experience the following effects.
Incapacitated. You have the Incapacitated condition.
Speed 0. Your Speed is O and can't increase.
Saving Throws Affected. You automatically fail Strength and Dexterity saving throws.
Attacks Affected. Attack rolls against you have Advantage.
Automatic Critical Hits. Any attack roll that hits you is a Critical Hit if the attacker is within 5 feet of you.

PETRIFIED [CONDITION] ᴿᴬᵂ

While you have the Petrified condition, you experience the following effects.
Turned to Inanimate Substance. You are transformed, along with any nonmagical objects you are wearing and carrying, into a solid inanimate substance (usually stone). Your weight increases by a factor of ten and you cease aging.
Incapacitated. You have the Incapacitated condition. 
Speed 0. Your Speed is O and can't increase.
Attacks Affected. Attack rolls against you have Advantage.
Saving Throws Affected. You automatically fail Strength and Dexterity saving throws.
Resist Damage. You have Resistance to all damage.
Poison Immunity. You have Immunity to the Poisoned condition.

ᴮᴹ If you are Petrified for more than 7 days, you become Unconscious. When the Petrified condition ends, you gain 1 Exhaustion level and you are Blinded for 1 minute. You can make a DC 15 Constitution saving throw at the end of each of your turns. On a success, you are no longer Blinded.

POISONED [CONDITION] ᴿᴬᵂ

While you have the Poisoned condition, you experience the foIlowing effect.
Ability Checks and Attacks Affected. You have Disadvantage on attack rolls and ability checks.

PRONE [CONDITION]

While you have the Prone condition, you experience the following effects.
Restricted Movement. Your only movement options are to crawl or to spend an amount of movement equal to half your Speed (rounded down) to right yourself and thereby end the condition. If your Speed is 0, you can't right yourself. If you crawl, each foot of movement costs 1 extra foot (2 extra feet in Difficult Terrain).
Attacks Affected. You have Disadvantage on attack rolls. An attack roll against you has Advantage if the attacker is within 5 feet of you. Otherwise, that attack roll has Disadvantage, ᴮᴹ unless you are Huge or Gargantuan. 

RESTRAINED [CONDITION] ᴿᴬᵂ

While you have the Restrained condition, you experience the following effects.
Speed 0. Your Speed is O and can't increase.
Attacks Affected. Attack rolls against you have Advantage, and your attack rolls have Disadvantage.
Saving Throws Affected. You have Disadvantage on Dexterity saving throws.

SLOWED [CONDITION] ᴮᴹ 

While you have the Slowed condition, you experience the following effects:
Speed Affected. Your Speed is halved.
Defense Affected. -2 penalty to AC and Dexterity saving throws. 
Limited Actions. On your turns, you can take either an action or a Bonus Action, not both, and you can't take Reactions.
Number of Attacks Affected. If you take the Attack action, you can make only one attack, or one fewer attack if you have the Extra Attack feature or Multiattack.
Falling to 0 Hit Points. When regaining HP after falling to 0 Hit Points, you are Slowed until the end of your next turn.

STUNNED [CONDITION]

While you have the Stunned condition, you experience the following effects.
Incapacitated. You have the lncapacitated condition.
ᴮᴹ Stupefied. Your Speed is Halved and you can speak only falteringly (no spellcasting).
Saving Throws Affected. You automatically fail Strength and Dexterity saving throws.
Attacks Affected. Attack rolls against you have Advantage.
ᴮᴹ Adrenaline Recovery. If you fail three saving throws against the same instance of this condition, you have Advantage on further saving throws made to end it.

The 5.24 PHB nerfed the Stunned condition by removing the "you can't move and can speak only falteringly" effect. For verisimilitude, my version limits the creature's Speed but does not prevent movement entirely. 

SUFFOCATION [HAZARD]

A creature can hold its breath for a number of minutes equal to 1 plus its Constitution modifier (minimum of 30 seconds) before suffocation begins. When a creature runs out of breath or is choking, it gains 1 Exhaustion level at the end of each of its turns. When a creature can breathe again, it removes all levels of Exhaustion it gained from suffocating.

SURPRISED [CONDITION]

If you are caught unaware by the start of combat, you are Surprised and experience the following effects.
Unprepared. When you roll Initiative, you have Disadvantage on the roll.
ᴮᴹ Flat-footed. You can't take a Reaction until the start of your turn.

The DM determines who might be surprised. If neither side tries to be stealthy, they usually notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side (-5 Passive Perception score in Dim Light). A character or monster that doesn't notice a threat is surprised at the start of the encounter. A member of a group can be surprised even if the other members aren't. 

SWALLOWED [HAZARD] ᴮᴹ 

While you are Swallowed by a creature, you experience the following effects:
Blinded and Restrained. Unless the swallowing creature is Gargantuan or its stat block says otherwise, you are Blinded and Restrained. However, if you attack with a Light weapon that deals Piercing or Slashing damage, you are considered neither Blinded or Restrained for that attack.  
Total Cover. You have Total Cover against attacks and other effects originating outside the creature that swallowed you. You have Disadvantage on Wisdom (Perception) checks made to hear.
Digestive Damage. At the end of each of your turns, you take damage as specified in the swallowing creature's stat block, or 10 (3d6) Acid damage if the stat block doesn't specify it.
Escaping. The stat block provide rules for escaping the creature. If not, the following applies: if the creature takes 20 damage or more on a single turn from a creature inside it, or the first time it becomes Bloodied, it must make a DC 15 Constitution saving throw. On a failed save, it regurgitates all swallowed creatures, which fall Prone in a space within 10 feet of the creature. If the creature dies, a swallowed creature can escape from the corpse by using half their movement, exiting Prone.

UNCONSCIOUS [CONDITION]

While you have the Unconscious condition, you experience the following effects.
Inert. You have the Incapacitated and Prone conditions, and you drop whatever you're holding. When this condition ends, you remain Prone.
Speed 0. Your Speed is O and can't increase.
Attacks Affected. Attack rolls against you have Advantage.
Saving Throws Affected. You automatically fail Strength and Dexterity saving throws. Automatic Critical Hits. Any attack roll that hits you is a Critical Hit if the attacker is within 5 feet of you.
Unaware. You're unaware of your surroundings. ᴮᴹ If you are Unsconscious because you are sleeping, decrease your Passive Perception score by 10.

An Unconscious creature can't choose to fail a saving throw, or consent to anything.

UNDERWATER COMBAT ᴮᴹ 

A fight underwater follows these rules. See also Suffocation [hazard]. 
Impeded Weapons. When making a melee attack roll with a weapon underwater, a creature that lacks a Swim Speed has Disadvantage on the attack roll unless the weapon deals Piercing or Psychic damage. A ranged attack roll with a weapon underwater has Disadvantage against a target within normal range, and automatically misses a target beyond the weapon’s normal range.
Fire Resistance. Anything underwater has Resistance to Fire damage.
Limited Spellcasting. Whenever a creature casts a spell with a Verbal component underwater, it must succeed on a DC 13 Intelligence (Arcana) check. On a failure, the muffled words and unstable magic trigger a Wild Magic Surge. On a natural 1, the spell fails outright and the spell slot or limited use feature is wasted.
Air Restriction. A creature that cannot breathe water can cast only one spell with a verbal component before it must surface for air.
Lightning Radius. Spells or effects that deal Lightning damage spread outward in water. Replace the effect’s normal area with a sphere centered on the point of origin: 10-foot radius per spell level (maximum 60 feet). The sphere affects all creatures in range, ally or foe, unless the spellcaster uses a special feature such as Sculpt Spell or Careful Spell. 
Deep Water (100+ feet). After each hour of swimming in deep water, a creature that lacks a Swim Speed must succeed on a DC 13 Constitution saving throw or gain 1 Exhaustion level.
Sonic Damage. Creatures take double Thunder damage (Vulnerability) while in deep water, due to amplified soundwave pressure. A creature that can magically breathe water or for which deep water is a natural environment ignores this vulnerability.
Visibility Underwater. Visibility underwater depends on water clarity and the available light. Use the Underwater Encounter Distance table to determine the encounter distances underwater. No natural light reaches below 200 ft.

Underwater Encounter Distance

Visibility	Encounter Distance
Clear water, Bright Light	60 feet
Clear water, Dim Light	30 feet
Murky water or Darkness	10 feet

POSSESSED [CONDITION] ᴮᴹ

While you have the Possessed condition, you experience the following effects.

Effects on the Host
Charmed. You are Charmed by your possessor.
Dual Nature. You count as both your normal creature type and the possessor’s creature type for the purpose of spells and effects.
Shared Resilience. You gain Resistance to one damage type the possessor resists or is immune to (DM’s choice).
Alien Intellect. You adopt the possessor’s Intelligence score and saving throw modifier, if they are higher than yours.
Vulnerable Vessel. The possessor can attempt to seize complete control of your body (see Control, below).
Molded Personality. For each week you are possessed, you gain a new personality trait or character flaw related to your possessor's identity. 

Effects on the Possessor
Ethereal Presence. The possessor cannot be directly targeted by attacks or spells while within you, except by effects that specifically affect both its creature type and its incorporeal essence. Spells or abilities that require sight cannot target it unless the attacker can perceive its hidden form, such as Divine Sense or Truesight.
Boon or Bane. At will, the possessor can grant a +1d4 bonus or impose a –1d4 penalty to any d20 test you make.
Mind Probe (2/day). The possessor may probe your surface thoughts and memories, as if casting Detect Thoughts. You can resist with a Wisdom saving throw.
Control (3/day). The possessor may fully control your body for 10d10 minutes (no saving throw), using its own Intelligence, Wisdom, Charisma, and skill proficiencies. 

While Controlled 
Helpless Awareness. You remain conscious of your surroundings but cannot act, speak, or move unless allowed by the possessor. 
Alignment Shift. Your alignment temporarily shifts to match the possessor’s.
Borrowed Tongues. You understand and can speak the possessor’s languages.
Surface Only. The possessor cannot access your deepest memories or secrets, only surface thoughts and emotions, except with its Mind Probe ability (see above).
During Combat: Each time you take damage while controlled, you may attempt a Charisma saving throw. On a success, the possession is suppressed for 1 minute.
Persistent Resistance: If you succeed on three of these saves within 24 hours, the possessor cannot attempt to control you again until you complete a Long Rest.

Suppressing the Possession
Rest Resistance. After each Long Rest, you may repeat the Charisma saving throw. On a success, the condition is suppressed until the end of your next Long Rest. You make this save with Disadvantage if you are on an Evil-aligned Outer Plane.
Moment of Defiance. If compelled to act against your values, you can use your Reaction to attempt a Charisma saving throw. On a success, the condition is suppressed for 1d4 hours.

A saving throw DC equals 10 + half the possessor's Challenge Rating (minimum 12). 

Ending the Condition
Possessing entities are expelled from bodies through divine spells or rituals, such as en exorcism.

See Mantra's Guide to Exorcism and Possession (homebrew "magic item" in D&D Beyond) for detailed rules about possession -- including initial saving throws to avoid the condition and exorcism rules to end it. 

INTOXICATION 

Alcohol and certain toxins can impair creatures in escalating ways. Intoxication has three distinct conditions— Buzzed, Drunk, and Wasted—each of which is cumulative with the previous stage. A creature’s stage reflects its current level of inebriation, with minor perks at low levels and serious drawbacks as intoxication deepens. Dwarves and creatures with Resistance or Immunity to the Poisoned condition requires twice the amount of alcohol before being affected by the Intoxication conditions.

BUZZED [LEVEL 1]

While you are Buzzed, you experience the following effects:
Relaxed. You have Disadvantage on Wisdom checks, and your Passive Perception score decreases by 5.
Liquid Courage. You gain 1d4 Temporary Hit Points and a +1d4 bonus on Charisma checks. These rolls are made with Disadvantage while Buzzed.

DRUNK [LEVEL 2]

While you are Drunk, you experience the following effects in addition to those of Buzzed:
Slurred. You are Poisoned (unless immune to the Poisoned condition).
Unsteady. You gain 1 Exhaustion level. This level is removed when you are no longer Drunk.
Bravery or Foolishness. You gain a +1d6 bonus on saving throws to avoid or end the Frightened condition. These rolls are made with Disadvantage if Poisoned.

WASTED [LEVEL 3]

While you are Wasted, you experience the following effects in addition to those of Drunk and Buzzed:
Overwhelmed. You gain 2 additional Exhaustion levels. These levels are removed when you are no longer Wasted.
Loss of Balance. At the start of each of your turns, you must succeed on a DC 10 Dexterity saving throw or fall Prone. On a natural 1, you also vomit and become Incapacitated for 1d4 turns.
Blackout. If you keep drinking and remain Wasted for more than 2 hours, you make a DC 13 Constitution saving throw or fall Unconscious for 1d4 hours. You wake early if you take damage or if a creature uses its action to rouse you.

Recovery

Each hour: Step down 1 stage (Wasted → Drunk → Buzzed → Sober).
Lesser Restoration: Reduce intoxication by 1 stage.
Greater Restoration or Long Rest: Ends intoxication.
If you were Wasted, you stay Poisoned for 1d4 hours (hangover).

 

Quote from SentientSteel >>

Yeah these are all really awesome, will definetly be using some of these, although Im not the DM for your players but, does rules 25 for 5e really... work out?

 

 There has been no issue so far. Is there a particular rule that seems problematic for you or your players ?

Oh no I was just surprised, all of these were really good rules and I guess im just not used to rules like 25... maybe i should run it sometime!