• Take the rules on the magic card as literal as possible.
• If there are rules in parts of a card that would affect a magic player, It would only effect a magic player. An opponent without an upkeep, phase, or step, is unaffected by cards that point out those.
• Organically translate the rulings on cards to the D&D session. If too many hoops must be jumped through to make a card work, the card may be too complex for integration. Best option is to ban their use.
• Summoned creatures are placed at the bottom initiative order. Multiple summoned magic card creatures attack at the same time.
• Creatures you summon that have a low Intelligence score, under the affects of Dominate Person, Dominate Monster, Dominate Beast, or Animate Dead are considered under your control.
• All destroy effects have a Constitution saving throw with  DC of 20 minus CMC of the card or be turned to ash.
• Power and toughness are converted to Health and damage roll via a 1d4 Rule
  A 4/4 turns into a 4d4 damage roll and 4d4 health.
• Life gain life loss is based on the 1d4 system as well. 10 life lost is equal to 10d4 life lost.
• First-strike: Creatures with first-strike are moved to the up initiative order. Multiple instances of first-strike attack at the same time.
• Haste: Creatures with haste may roll for initiative.
• Trample: Creatures with trample ignore AC
• Death-touch: upon a successful attack roll Constitutions Save with a DC of 20 minus CMC of card or be turned to ash.
• Double-strike: Treat Double-strike as first-strike and a standard attack. One attack at the top of initiative and one at the bottom.
• Flash: You may use you reaction to cast a spell with flash
• Flying: As if the flight spell is cast on a creature
• Hex-proof: Immune from magic effects and weapons from an opponents.
• Indestructible : Immune to all forms of damage to HP
• Life-link: Functions the same as in MtG
• Protection from creatures: Immune from all damage and spells cast by creatures.
• Shroud: Immunity to magic
• Bushido: The effects of Bushido trigger when attacked or attacks and dissipate after.
• Rampage: When this creature is attacked, It gain +X/+X
• Afflict: When you attack, your target takes half of your damage die , initially.
• Melee: At the beginning this creature's turn, It gains +X/+X, where X is the number of creatures that made an attack before it in the initiative order.
• Skulk: If a creature has more damage potental then the creature with shulk, a creature with Shulk ignores the base 10 in a the AC.
• Unleash: If you unleash a creaure, it gain a +1/+1 counter, but reduces the creatures AC to 0.
• Regenerate: Protection form Destruction effects.
• Vigilance: Any number of attacks of opportunity
• More rulings will be made as the game progresses and all rules are subject to change.

When it comes down to it, this is just a really complex and powerful magic item. Would love to hear your thoughts. Would love to hear criticism. Constructive criticism, if you can.  

Or just forget all that balancing nightmare and just stick to Guildmaster's Guide to Ravnica, since it's based on Magic: The Gathering? Seems easier.