Living Brain, Mechanical Marvel

At the beginning of combat on your turn, target non-Equipment artifact you control becomes an artifact creature with base power and toughness 3/3 until end of turn. Untap it.

Island

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Sol Ring

Impostor Syndrome

Whenever a nontoken creature you control deals combat damage to a player, create a token that's a copy of it, except it isn't legendary.

Ego Erasure

Changeling (This card is every creature type.)
Creatures target player controls get -2/-0 and lose all creature types until end of turn.

Undercover Operative

You may have this creature enter 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.)

Three Tree Mascot

Changeling (This card is every creature type.)
{1}: Add one mana of any color. Activate only once each turn.

Deceptive Frostkite

Flying
You may have this creature enter as a copy of a creature you control with power 4 or greater, except it's a Dragon in addition to its other types and it has flying.

Sakashima of a Thousand Faces

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

Universal Automaton

Changeling (This card is every creature type.)

Mothdust Changeling

Changeling (This card is every creature type.)
Tap an untapped creature you control: This creature gains flying until end of turn.

Krovikan Mist

Flying
Krovikan Mist's power and toughness are each equal to the number of Illusions on the battlefield.

Alchemax Slayer-Bots

When this creature enters, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Naga Fleshcrafter

You may have this creature enter as a copy of any creature on the battlefield.
Renew — {2}{U}, Exile this card from your graveyard: Put a +1/+1 counter on target nonlegendary creature you control. Each other creature you control becomes a copy of that creature until end of turn. Activate only as a sorcery.

Mysterio, Master of Illusion

When Mysterio enters, create a 3/3 blue Illusion Villain creature token for each nontoken Villain you control. Exile those tokens when Mysterio leaves the battlefield.

Lord of the Unreal

Illusion creatures you control get +1/+1 and have hexproof. (They can't be the targets of spells or abilities your opponents control.)

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Clone

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

Metallic Mimic

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Each other creature you control of the chosen type enters with an additional +1/+1 counter on it.

Flying Octobot

Flying
Whenever another Villain you control enters, put a +1/+1 counter on this creature. This ability triggers only once each turn.

Phantasmal Image

You may have this creature enter 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."

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Mechanical Mobster

When this creature enters, exile up to one target card from a graveyard. Target creature you control connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on that creature.)

Doc Ock's Henchmen

Flash
Whenever this creature attacks, it connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)

Spark Double

You may have this creature enter 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.

Changeling Wayfinder

Changeling (This card is every creature type.)
When this creature enters, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.

Mysterio's Phantasm

Flying, vigilance
Whenever this creature attacks, mill a card. (Put the top card of your library into your graveyard.)

Bloodline Pretender

Changeling (This card is every creature type.)
As this creature enters, choose a creature type.
Whenever another creature you control of the chosen type enters, put a +1/+1 counter on this creature.

Sakashima's Student

Ninjutsu {1}{U} ({1}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
You may have this creature enter as a copy of any creature on the battlefield, except it's a Ninja in addition to its other creature types.

Mystic Reflection

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter this turn, they enter as copies of the chosen creature.
Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Glasspool Shore

Glasspool Mimic

You may have this creature enter as a copy of a creature you control, except it's a Shapeshifter Rogue in addition to its other types.

Glasspool Mimic // Glasspool Shore

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Ghastly Mimicry

Enchant creature
At the beginning of your upkeep, create a token that's a copy of enchanted creature, except it's a Spirit in addition to its other types.
If Ghastly Mimicry would be put into a graveyard from anywhere, exile it instead.

Mirrorhall Mimic

You may have this creature enter as a copy of any creature on the battlefield, except it's a Spirit in addition to its other types.
Disturb {3}{U}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Mirrorhall Mimic // Ghastly Mimicry

Barkform Harvester

Changeling (This card is every creature type.)
Reach
{2}: Put target card from your graveyard on the bottom of your library.

Renegade Doppelganger

Whenever another creature you control enters, you may have this creature become a copy of that creature until end of turn. (If it does, it loses this ability for the rest of the turn.)

The Clone Saga

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Surveil 3.
II — When you next cast a creature spell this turn, copy it, except the copy isn't legendary.
III — Choose a card name. Whenever a creature with the chosen name deals combat damage to a player this turn, draw a card.

Beetle, Legacy Criminal

Flying
{1}{U}, Exile this card from your graveyard: Put a +1/+1 counter on target creature. It gains flying until end of turn. Activate only as a sorcery.

Lady Octopus, Inspired Inventor

Whenever you draw your first or second card each turn, put an ingenuity counter on Lady Octopus.
{T}: You may cast an artifact spell from your hand with mana value less than or equal to the number of ingenuity counters on Lady Octopus without paying its mana cost.

Hydro-Man, Fluid Felon

Whenever you cast a blue spell, if Hydro-Man is a creature, he gets +1/+1 until end of turn.
At the beginning of your end step, untap Hydro-Man. Until your next turn, he becomes a land and gains "{T}: Add {U}." (He's not a creature during that time.)

Gigantoplasm

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

Waxen Shapethief

Flash
You may have this creature enter as a copy of an artifact or creature you control.
Cycling {2} ({2}, Discard this card: Draw a card.)

Body Double

You may have this creature enter as a copy of any creature card in a graveyard.

Mockingbird

Flying
You may have this creature enter as a copy of any creature on the battlefield with mana value less than or equal to the amount of mana spent to cast this creature, except it's a Bird in addition to its other types and it has flying.

Copycrook

You may have this creature enter as a copy of any creature on the battlefield, except it has "Whenever this creature attacks, it connives." (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)

Mirror Gallery

Clever Impersonator

You may have this creature enter as a copy of any nonland permanent on the battlefield.

Helm of the Host

At the beginning of combat on your turn, create a token that's a copy of equipped creature, except the token isn't legendary. That token gains haste.
Equip {5}

Chameleon, Master of Disguise

You may have Chameleon enter as a copy of a creature you control, except his name is Chameleon, Master of Disguise.
Mayhem {2}{U} (You may cast this card from your graveyard for {2}{U} if you discarded it this turn. Timing rules still apply.)

Irenicus's Vile Duplication

Create a token that's a copy of target creature you control, except the token has flying and it isn't legendary.

Amoeboid Changeling

Changeling (This card is every creature type.)
{T}: Target creature gains all creature types until end of turn.
{T}: Target creature loses all creature types until end of turn.

Mistwalker

Changeling (This card is every creature type.)
Flying
{1}{U}: This creature gets +1/-1 until end of turn.

Wayfarer's Bauble

{2}, {T}, Sacrifice this artifact: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Infinite Reflection

Enchant creature
When this Aura enters attached to a creature, each other nontoken creature you control becomes a copy of that creature.
Nontoken creatures you control enter as a copy of enchanted creature.

Vizier of Many Faces

You may have this creature enter as a copy of any creature on the battlefield, except if this creature 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}

Mirror Box

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.

Distant Melody

Choose a creature type. Draw a card for each permanent you control of that type.

Doc Ock, Sinister Scientist

As long as there are eight or more cards in your graveyard, Doc Ock has base power and toughness 8/8.
As long as you control another Villain, Doc Ock has hexproof. (He can't be the target of spells or abilities your opponents control.)

Omni-Changeling

Changeling (This card is every creature type.)
Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
You may have this creature enter as a copy of any creature on the battlefield, except it has changeling.

Phyrexian Metamorph

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

Mirror Image

You may have this creature enter as a copy of a creature you control.

Hulking Metamorph

Prototype {2}{U}{U} — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
You may have this creature enter as a copy of an artifact or creature you control, except it's an artifact creature in addition to its other types, and its power and toughness are equal to this creature's power and toughness.

Stunt Double

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

Visage Bandit

You may have this creature enter as a copy of a creature you control, except it's a Shapeshifter Rogue in addition to its other types.
Plot {2}{U} (You may pay {2}{U} and exile this card from your hand. Cast it as a sorcery on a later turn without paying its mana cost. Plot only as a sorcery.)

Spider-Slayer, Hatred Honed

Whenever Spider-Slayer deals damage to a Spider, destroy that creature.
{6}, Exile this card from your graveyard: Create two tapped 1/1 colorless Robot artifact creature tokens with flying.