msem-instigator

Enchant creature
Enchanted creature can't be blocked.
{1}{G}: Enchanted creature gets +1/+1 and gains hexproof until end of turn.

Whenever Uncanny Allocator enters or attacks, give any number of permanents and/or players with counters on them another counter of each kind already there.

Unceasing Flames deals X damage to any target, where X is 2 plus the number of cards named Unceasing Flames in your graveyard.
Conjure three cards named Unceasing Flames and shuffle them into your main library.

Whenever a creature you control is dealt damage, put a +1/+1 counter on that creature.

When Uncovered Mine enters and at the beginning of your upkeep, return a random card from your graveyard to your hand.

When Undead Archivist enters, return target instant or sorcery card from your graveyard to your hand.
Revive {5}{U} ({5}{U}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

When Undead Banneret enters, if you control a legendary creature, each opponent loses 4 life.

This spell costs {1} less to cast for each Zombie creature card in your graveyard.
When Undead Harbinger enters, return target Zombie card from your graveyard to your hand.

You may have Undecided Mimic enter or phase in as a copy of any creature on the battlefield, except it has this ability and “{2}{U}{U}: Undecided Mimic phases out.” (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

If you've scried this turn, this spell costs {2} less to cast and can't be countered.
Draw two cards.

Enchant creature
Enchanted creature gets +1/+0 and has menace. (That creature can't be blocked except by two or more creatures.)

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Undercity Diplomat can't be blocked by marked creatures.

{T}, Sacrifice a permanent: Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

This spell costs {1} less to cast for each artifact you control. (This applies before Treasures are sacrificed for mana.)
When Underhanded Deal enters, draw three cards.
Whenever you cast a spell, you lose 1 life.

{T}, Pay 1 life: Add one mana of any color that a land an opponent controls could produce.

As an additional cost to cast this spell, exile a creature card from your graveyard.
You draw three cards and you lose 3 life.

Enchant creature
Enchanted creature has first strike. (That creature deals combat damage before creatures without first strike.)

Undine Coven gets +1/+1 for each other Merfolk you control.
Whenever you cast a noncreature spell, Undine Coven deals 1 damage to target player or planeswalker.

Return up to two target creature cards with total mana value 4 or less from your graveyard to the battlefield.

Mill four cards, then return any number of creature cards with total mana value 4 or less from your graveyard to the battlefield.

Creatures you control get +2/+0 and have deathtouch as long as ten or more cards are in your graveyard.

Whenever a creature you control dies, you may return all cards that were inscribed onto that creature and all Auras that were attached to that creature to their owners' hands.

Unending Slime enters with X +1/+1 counters on it.
{2}{G}{G}{G}: Return Unending Slime from your graveyard to your hand.

Search your library for up to four basic land cards, reveal them, put them into your hand, then shuffle. You may play an additional land this turn.

Flying
When Unfettered Atrocity enters, destroy target creature or planeswalker.