msem-instigator

At the beginning of your upkeep, reveal the top card of your library. If it has the same name as a card in your graveyard, put the revealed card into your hand. Otherwise, put it into your graveyard.

Colossal 2—{4}{B} (You may cast this for its colossal cost to have it enter with two +1/+1 counters; or pay {4}{B} as a sorcery: Put two +1/+1 counters on it if it has none.)
Lifelink

When Undying Lich dies, create a 6/3 black Zombie Horror creature token with menace and “When this creature dies, create an 8/5 black Elder Demon Horror creature token with flying, deathtouch, and menace.”

Ungoverned Sneak can't be blocked by creatures with greater power.
Attain {3}{U} ({3}{U}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

{T}: Add one mana of any color.
{T}, Sacrifice Unicorn of the Vale: Add three mana of any one color.

Whenever you cast a noncreature spell, create a 1/1 colorless Construct artifact creature token.

{G/W}: If Unlikeliest Heroes doesn't have a +1/+1 counter on it, put a +1/+1 counter on it.
{2}{G/W}{G/W}: If Unlikeliest Heroes has a +1/+1 counter on it and doesn't have vigilance, put two +1/+1 counters and a vigilance counter on it.
{3}{G/W}{G/W}{G/W}: If Unlikeliest Heroes has vigilance and not indestructible, put four +1/+1 counters and an indestructible counter on it.

Flying
Whenever you cast a spell from your graveyard, return Unliving Swarm from your graveyard to your hand.

When Unmasker of Fate's Design enters, look at target player's hand. Choose a nonland card from it and exile that card with a puzzle counter on it. As long as that card has a puzzle counter on it, that player may pay {2} and 1 life at any time. If they do, return the exiled card to their hand.

Trample
Whenever Unruly Cannoneer crews a Vehicle, that Vehicle gets +1/+1 and gains trample until end of turn.

Prowess
Whenever Unseen Hand attacks, exile target noncreature, nonland card with mana value 1 or less from your graveyard. Copy that card. You may cast the copy. (You still pay its costs.)

Discard a card: Unseen Maniac gets +1/+1 and can't be blocked this turn.
Whenever Unseen Maniac deals combat damage to a player, draw a card.

Glitch—Sacrifice a creature. (Remove one [restriction] for each time you pay the glitch cost.)
When Unshackled Revolutionary enters, you may destroy target creature an opponent controls [with mana value 3 or less]. [You lose 3 life.]

Flash
Deathtouch

{T}: Target attacking or blocking creature gets +1/+1 until end of turn.

Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)

Unwavering Questant can't block.
When an opponent fails a trial, return Unwavering Questant from your graveyard to the battlefield.

When Unwitting Fanatic enters, create a 3/2 colorless Horror creature token.
Sacrifice Unwitting Fanatic: Another target permanent you control gains hexproof and indestructible until end of turn.

When Urisk Fiddler enters, draw a card.

First strike (This creature deals combat damage before creatures without first strike.)

Whenever V-4 Fixit or another artifact you control enters, target creature you control gets +1/+1 until end of turn.

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
When Vaeldan's Liberator dies, you may exile it. If you do, return a permanent card with mana value less than or equal to Vaeldan's Liberator's power from your graveyard to your hand.

Valeron Vanguard can't be blocked by 1/1 creatures.

Motivate 1 (When this creature enters, you may motivate target creature with less power than this by putting a +1/+1 counter on it.)
{2}{W}{W}: Exile Valtrian Cavalier, then return it to the battlefield under your control.

Vampire Partaker can't block.
Sacrifice a creature: Put a +1/+1 counter on Vampire Partaker. You gain 1 life. Activate only as a sorcery.