We all change something from the standard rules for example my house rule for crits is you roll normally add all the stuff then double it, so 1d8+4 you roll a 4 then plus 4 so 8 then double 8 to 16. You can also crit on saving throws if they roll a nat 1. Now please tell me your unique house rules!

At my table, fractional damage is rounded down (as normal) against monsters & NPCs, but rounded up against PCs, just to put a little extra pressure on them:

It my games I have seen far too many low roll crits. "Yes! NAT 20! *clatter* 3 damage...."

The solution was max damage die, then roll, then add bonuses. So 1d8+3 on a crit would be 8 +1d8 +3.

Applies to both PCs and monsters.

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Picking up a dropped item or weapon costs and Action. Might change to Action or Bonus Action. RAW it costs nothing to pick up a dropped weapon but I want Disarm to matter.

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Stand up from Prone costs all of your Movement or Your Action. Again I want there to be substantial cost/benefit.

Dunno if you'd count these as weird houserules, but these are some my groups use:

First, we were a little disappointed 5th edition dropped critical failures/successes on ability checks so we tend to play with the following:

• Critical Failure: A natural 1 on a check is a failure no matter what your bonus is, because no matter how good you are at something you can always mess it up somehow. This includes characters with Reliable Talent or similar (so these only improve a roll of 2-9), as a College of Eloquence Bard can still say the wrong name, or accidentally imply someone looks like a gelatinous cube by attempting an overly clever turn of phrase in a second language etc.
• Critical Success: A natural 20 on a check is a success no matter what the DC was, but it's a "mixed success", so if the party's Barbarian with -1 Charisma tries to blag their way past a guard they might make an argument so unexpectedly convincing that the guard doesn't know what to do (isn't letting you through unquestioningly, but isn't kicking you out either).

We also tend to run that a critical miss on an attack requires you to roll an additional d6, on a second 1 something bad happens; if you're attacking with a weapon it means the weapon is compromised somehow (a sword may be dropped, a bowstring may snap etc.), or if an ally was near to your target then you may hit them instead, it's situational.

Since we sometimes have difficult combats, we allow drinking a potion as a bonus action, but administering one still requires an action.

Probably the weirdest rule is that rule of cool almost always wins; if something is cool and not too silly then you can always attempt it, and a decently successful roll allows it happen. I'm not sure if this really counts as a house-rule as I feel like it's how D&D is supposed to be run but it's good to make it clear in a group that you're never bound by only what your character sheet says you can do, so long as you can justify it.

We've also been trying to adopt the Critical Role "how do you want to do this?" type finishing moves, i.e- if someone scores the killing blow on a significant enemy (large, elite, named etc.) they get to describe exactly how they finish them off. It's a good way to encourage players to describe what they're doing more, which I think games with my current groups have been lacking a bit (I like to do it regardless but I think it adds to the game when more players do).

Quote from Haravikk >>

 

Since we sometimes have difficult combats, we allow drinking a potion as a bonus action, but administering one still requires an action.

 

This is a different from RAW. It is quite popular in literature to have healing potions work whether they are consumed or poured over a wound. I can see the appeal.

Potion sickness: if you consume more than 1 potion within 24hrs the affect of the potion still works but your health slowly degrades over time, affects also very on strength and type of potion. Eg: reg potion used more than once in a day is 1d4 every 4 hours per extra potion used and will wear off after 2 days. This forces the player to take more short rests to recover because they become sick hindering them and party within the story. (Especially fun for the parties with no healer)

Quote from Wysperra >>

Quote from Haravikk >>

Since we sometimes have difficult combats, we allow drinking a potion as a bonus action, but administering one still requires an action. 

This is a different from RAW. It is quite popular in literature to have healing potions work whether they are consumed or poured over a wound. I can see the appeal.

Sure, I think I first saw this houserule being used on Critical Role where they sometimes have really tough combats where this kind of thing is needed. We also partly adopted it because my usual group don't really consider party balance and I got tired of building characters to fill the gaps rather than just playing what I wanted to heh, so it's a good rule to have when there's no "proper" healer in the party.

Again not sure how "weird" it is, but another rule we've been trialing recently is multiple hit blasts; when characters have good blast spells but only a single target it can be really limiting, so we're trying a rule whereby targets that are Large or bigger can be hit a number of times equal to the squares they occupy rounded down, so a Large creature can be hit twice, Huge four times, and Gargantuan eight times. When rolling for attacks/saves the creature's near side squares provide cover to squares further back, and attacks/saves are resolved "in order" with the first missed attack or passed save ending the sequence.

It's a bit complicated to get your head around at first but in practice so far it feels fairly common sense; for example, let's so you hit a Gargantuan creature in the front with a fireball, the first four squares are definitely hit, and you might hit some on the sides since fireball wraps around corners, but those will gain some cover from the front. So you'd roll eight saves starting form the front. We tend to use digital rollers so we can just roll them all at once and look at the saves in order, if you have a mix of dice colours you could define an order (e.g- lightest to darkest) so you can roll multiple at once. If the first save fails you resolve the second and so-on until there's a success, so it's possible the creature will dodge really well and only take half damage, or it might fail multiple and take several rounds of damage.

This does put a bit of a burden on the DM for balancing, since a party with a lot of access to blasts might destroy large single targets more easily, but that's kind of the balancing act DMs need to do anyway (some enemies have abilities that can ruin specific parties and vice versa).