The "legend rule" doesn't apply to permanents you control. Each legendary creature you control gets +1/+1. Each nontoken creature you control gets +1/+1 for each other creature you control with the same name as that creature.

This spell can't be countered. You may have Altered Ego enter the battlefield as a copy of any creature on the battlefield, except it enters with X additional +1/+1 counters on it.

Mutate {5}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, tap up to X target creatures, where X is the number of times this creature has mutated. Those creatures don't untap during their controller's next untap step.

Mutate {5}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, exile cards from the top of your library until you exile X permanent cards, where X is the number of times this creature has mutated. Put those permanent cards onto the battlefield.

The "legend rule" doesn't apply to tokens you control. Whenever another nontoken legendary permanent enters the battlefield under your control, you may pay {1}. If you do, create a token that's a copy of it. That token gains haste. Sacrifice it at the beginning of the next end step.

Cephalid Facetaker can't be blocked. At the beginning of combat on your turn, you may have Cephalid Facetaker become a copy of another target creature until end of turn, except it's 1/4 and has "This creature can't be blocked."

You may have Clever Impersonator enter the battlefield as a copy of any nonland permanent on the battlefield.

You may have Clone enter the battlefield as a copy of any creature on the battlefield.

Mutate {3}{R} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Reach Whenever this creature mutates, you may discard a card. If you do, draw a card.

Mutate {2}{W}{W} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Lifelink Whenever this creature mutates, create two 1/1 white Cat creature tokens with lifelink.

You may have Dack's Duplicate enter the battlefield as a copy of any creature on the battlefield, except it has haste and dethrone. (Whenever it attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Mutate {3}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flying Whenever this creature mutates, draw a card.

Mutate {1}{G}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Reach, trample Whenever this creature mutates, destroy target artifact or enchantment an opponent controls.

You may have Gigantoplasm enter the battlefield as a copy of any creature on the battlefield, except it has "{X}: This creature has base power and toughness X/X."

Mutate {2}{W} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, other creatures you control get +X/+X until end of turn, where X is the number of times this creature has mutated.

Mutate {3}{R/G}{U}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flying, trample Whenever this creature mutates, exile cards from the top of your library until you exile a nonland permanent card. Put that card onto the battlefield or into your hand.

Mutate {U/R}{U/R} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, return target instant or sorcery card from your graveyard to your hand.

Mutate {3}{W} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Vigilance Whenever this creature mutates, you gain 4 life.

You may have Mercurial Pretender enter the battlefield as a copy of a creature you control, except it has "{2}{U}{U}: Return this creature to its owner's hand."

Mutate {2}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

You may have Mirror Image enter the battlefield as a copy of a creature you control.

Changeling (This card is every creature type.) You may have Moritte of the Frost enter the battlefield as a copy of a permanent you control, except it's legendary and snow in addition to its other types and, if it's a creature, it enters with two additional +1/+1 counters on it and has changeling.

Mutate {G}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) {1}, {T}: Look at the top card of your library. If it's a land card, you may put it onto the battlefield. If you don't put the card onto the battlefield, put it into your hand.

You may have Phantasmal Image enter the battlefield as a copy of any creature on the battlefield, except it's an Illusion in addition to its other types and it has "When this creature becomes the target of a spell or ability, sacrifice it."

({U/P} can be paid with either {U} or 2 life.) You may have Phyrexian Metamorph enter the battlefield as a copy of any artifact or creature on the battlefield, except it's an artifact in addition to its other types.

Mutate {2}{R} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) {T}: This creature deals X damage to any target, where X is the number of times this creature has mutated.

Mutate {3}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flash Whenever this creature mutates, you may return target creature an opponent controls to its owner's hand.

You may have Progenitor Mimic enter the battlefield as a copy of any creature on the battlefield, except it has "At the beginning of your upkeep, if this creature isn't a token, create a token that's a copy of this creature."

Mutate {1}{R/W}{R/W} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, other creatures you control get +2/+1 until end of turn.

You may have Sakashima of a Thousand Faces enter the battlefield as a copy of another creature you control, except it has Sakashima of a Thousand Faces's other abilities. The "legend rule" doesn't apply to permanents you control. Partner (You can have two commanders if both have partner.)

You may have Sakashima the Impostor enter the battlefield as a copy of any creature on the battlefield, except its name is Sakashima the Impostor, it's legendary in addition to its other types, and it has "{2}{U}{U}: Return this creature to its owner's hand at the beginning of the next end step."

Mutate {3}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Trample Whenever this creature mutates, destroy target noncreature permanent. Its controller creates a 3/3 green Beast creature token.

Mutate {1}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flash Whenever this creature deals combat damage to a player, draw a card.

Mutate {5}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flying Whenever this creature mutates, gain control of target noncreature artifact.

You may have Spark Double enter the battlefield as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary.

Flash You may have Stunt Double enter the battlefield as a copy of any creature on the battlefield.

Mutate {3}{G/U}{G/U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, create a 3/3 green Beast creature token.

You may have Undercover Operative enter the battlefield as a copy of any creature on the battlefield, except it enters with a shield counter on it if you control that creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)

Mutate {1}{W/U}{R}{R} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Flying, first strike Whenever this creature mutates, you may cast target noncreature card with mana value 3 or less from your graveyard without paying its mana cost.

You may have Vizier of Many Faces enter the battlefield as a copy of any creature on the battlefield, except if Vizier of Many Faces was embalmed, the token has no mana cost, it's white, and it's a Zombie in addition to its other types. Embalm {3}{U}{U}