Hi guys. I'm about to start DMing a Homebrew campaign set in the MTG Universe. It's my first campaign. I have play tested the rules and polished them a little just wanted another opinion on them. So it is using 5e rules plus some others. Each PC has either one or two mana colours. The PCs can cast Enchantment, Sorcery and Instant Cards that use these colours. I made a table which shows how much mana and spells they have at different levels:

Cards that become a cantrip can be cast without spending the mana. Mana resets after a long rest.

Also I made these rules for keywords in MTG:

MTG Zone Conversion:

• Library: Your full list of abilities and spells that you can access at your current level. May be used sometimes as Hand as well.

• Hand: Has two portrayals, mainly the spell/ability list you can access (Symbolised as what you can think of at the moment, hence the addition to INT or WIS upon drawing a card). The other will be your PC’s hand, for times like discarding hand making you drop what your holding. (Dependent on the DM decision)
• Graveyard: Your spent spells and abilities that have a cooldown cost.
• (All other zones are already in D&D, Self-explanatory, or not being used)

Effects of MTG Keywords:

• Aftermath: Spells cast with this must have their joined card already cast to be able to be used.

• Annihilator: Defenders against a creature with Annihilator X sacrifice X abilities between the allies of the defenders.
• Bolster: Amongst allies of the source of Bolster X, the one with the lowest AC gains +X to AC and +X to attack rolls for the remainder of the encounter.
• Buyback: When casting card pay the buyback cost to retain the card in the prepared spells list. Otherwise it can not be used again until a long rest has been taken

• Convoke: “Tapping” allies can be used in the mana cost of a convoke spell. The allies must be willing.

• Crew: If an actual “Artifact - Vehicle” card is found or used, the crew cost on the card is the amount of people that are needed to drive it.
• Cumulative upkeep: If a card has a cumulative upkeep cost you may keep it being cast per turn by paying the cost. Otherwise it is used and cannot be used again until it’s corresponding cooldown is paid.
• Cycling: If a card has cycling you may pay that cost instead and gain a +1 to a skill modifier to a skill decided by a d6. (STR 1, CON 2, DEX 3, INT 4, WIS 5, CHA 6)

• Deathtouch: Causes necrotic damage of varying dice roll per turn until death occurs.

• Defender: Unable to make an attack action.

• Detain: Targets of must be within a 60 ft. radius of the source. Until the source’s next turn, those creatures can't attack or block and their activated abilities can't be activated. Other factors depending on source.

• Double Strike: Able to make two attack actions, ignoring AC on the first attack roll. Only a natural 1 would miss.

• Enchant: Make the target have a ability or effect based on a spell or card.

• Entwine: Theses spells have 2 abilities and the entwine cost must be paid for both to take effect.

• Equip: For artifact - equipment cards that convert to armour in D&D, if they are not already equipped before encounters start they must have their cost paid in either turns or mana to equip mid battle. Can be equipped outside battle for no cost. Equipping for a cost attunes for 1 round for equipment that requires attunement. For artifact - equipment cards that convert to weapons follow the usual rules for changing weapons. Cannot attune mid battle.

• Exile: For solo targets instantly die going to saving throws at a disadvantage. For multi-targets make a DC 10 + CON Constitution saving throw at a disadvantage. Only upon a fail does exile take effect.

• Fight: Targets have to be in a 20 ft. radius of each other. Targets of the spell both roll to hit with their main weapon. Upon a hit deals damage.

• First Strike: Only a natural one fails an attack roll.

• Flash: For a summoned creature means a instant surprise attack out of initiative order. For a spell means it can take effect as a reaction.

• Flying: Can cause creatures who do not innately fly have the ability to do so. Has  duration depending on the card.

• Haste: Goes next in initiative order, even in a surprise attack.

• Hexproof: Cannot be hit by spells, magical weapons or ranged attacks by an enemy source. Can still be the target of melee strikes with non-magical weapons, but they roll at a disadvantage.

• Indestructible: Cannot sustain damage while indestructible. Duration depends on the card which causes it.

• Kicker: A kicker cost may be paid to do additional abilities with spells.

• Lifelink: upon a successful attack roll gain 1 hit die back in health. Temp HP after maximum. Temp HP doesn't stack.

• Menace: Attack rolls attack you at a disadvantage unless an ally is within a 10 ft. radius.

• Multikicker: A kicker cost may be paid multiple times to do additional abilities with spells to the same amount of times.

• Prowess: When an action is used by an enemy uses a spell or attacks with a magical weapon you gain +1 to attack rolls and +1 to AC until end of turn.

• Reach: Melee attacks can reach 15 ft. Into the air to hit flying creatures.

• Regenerate: Pay the cost of the spell and regenerate full hp.

• Sacrifice: Causes the sacrifice of one of your spells or abilities that need a rest to be reused.

• Scry: Gain a +1 to either INT, or WIS modifiers for the remainder of the encounter. May add to another modifier instead but rolls a d6 decide. (STR 1, CON 2, DEX 3, INT 4, WIS 5, CHA 6)

• Tap: Causes target to fall prone, forcing them to use their action to stand up again.

• Trample: Any enemies in a 15ft radius of a successful attack roll recurve the same damage as target.

• Untap: Can be used to stand up from a prone position without using an action.

• Vigilance: Always have a bonus action available. Cannot be used for an action already taken this turn.

• Wither: All damage dealt by a creature with wither doesn’t affect HP but causes -X to AC and -X to attack rolls to the damaged creature. X equals the damage dealt.

• Protection: Damage can not be caused by a source that target has protection from.
• Regenerate: Upon paying the cost gain all hp back to maximum.
• Shroud: Cannot be the target of spells, ranged attacks and attacks caused by magical weapons regardless of the source. Can still be the source of melee attacks by non-magical weapons, but they roll attack at a disadvantage.

Further MTG Rule Conversions:

• Cards that add to power, add to the attack roll to the same amount on the card.
• Cards that add to toughness, add to AC to the same amount on the card.
• Land isn’t needed for mana, though cards that affect land, affects the land around you for 30 ft. Eg. The enchantment Forbidden Lore has the following effects in MTG “Enchant land. Enchanted land has ": Target creature gets +2/+1 until the end of turn." In D&D the enchantment would enchant a 30 ft. area of land. While the caster is in AOE they may fall prone and give an ally +1 to attack rolls and a +2 to AC until their next turn. May stay prone to continue the effect. Must use an action to get back up and another to re-target the spell.
• Drawing a card adds +1 to INT or WIS.
• Discarding makes it so that you cannot use one of your abilities/spells. They act as being used and must follow their cooldown procedures.
• Instants can be cast as reactions.
• Enchantments and sorceries can be cast only as the action on your turn.
• Artifact cards that have an attack follow the standard attack rolls and proficiencies for weapons unless otherwise stated in the card attributes file.

The campaign is starting in Zendikar. I'm using creature cards throughout the campaign as the monsters and npc. Artifact cards are scattered throughout. I've already added a few and converted them into D&D but are waiting to see what others my group would like to see at some point in the campaign before converting them. Normal D&D items are still in the campaign as well.

This post is a combination of showing off my rules I've thought of/getting some advice. Sorry for the long post and the formatting issues I have with it. If this is posted in the wrong spot or breaking rules that was not my intention and am happy to take it down/edit it accordingly. Any comments on the rules I've made for my campaign/questions on the rules are always welcome.

I am not sure how to convert MTG spell cards into spell slots or vice-versa.

Question: Are these rules meant to replace spellcasting rules, or are any characters allowed to use mana casting?

Our DM for a PbP added mana to his game.  It turned out to be a pretty good mechanic the way he implemented it. You can check out his homebrew rules here: https://www.dndbeyond.com/linkout?remoteUrl=http%3a%2f%2fhomebrewery.naturalcrit.com%2fshare%2fB1LPWO0lW