msem-instigator

Destroy target artifact or enchantment. You gain life equal to its mana value.

Target opponent sacrifices half the permanents they control, rounded down.

When Unburdening Priest enters, you may exile any number of creatures you control not named Unburdening Priest, then return those cards to the battlefield under your control.

Search your library for a permanent card with mana value X or less, reveal it, put it into your hand, then shuffle.

Target creature gets +1/+1 and gains double strike until end of turn. (That creature deals both first-strike and regular combat damage.)

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.

Spend only mana produced by Treasures to cast spells.
{2}, Discard a card: Create two Treasure tokens.

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.

Put two -1/-1 counters on target creature.
Agonize (You may cast this card from your graveyard by putting a -1/-1 counter on a creature you control in addition to paying its other costs. Then exile this card.)

This spell costs {2} less to cast if you control a Scout.
Search your library for up to two basic land cards, reveal those cards, and put one onto the battlefield tapped and the other into your hand, then shuffle.

Uncharted Haven enters tapped.
As Uncharted Haven enters, choose a color.
{T}: Add one mana of the chosen color.

Hexproof
When Uncharted Leviathan enters, target creature can't be blocked this turn.

Creatures your opponents control get -2/-0 until end of turn.
Draw a card.

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

Enspirit (As you cast this spell, you may exile a nonenchantment creature you control until this leaves the battlefield or fails to resolve. Reduce this spell's cost by the exiled card's mana value.)
Deathtouch

Target creature can't be blocked this turn.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “r3—You may cast a copy of this card from exile without paying its mana cost.”)

Look at the top two cards of your library. Put one of them into your hand, then you may have any number of players each mill three cards.

When Uncovered Idol enters, scry 1.
{1}, Sacrifice Uncovered Idol: Put a +1/+1 counter on target creature. Activate only as a sorcery.

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

When Uncovered Secrets enters, search your library for an artifact card, reveal that card, then shuffle and put that card on top.
Concord — Creatures you control get +1/+1 as long as there are four or more card types among permanents you control.

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.

Creature cards in your graveyard have revive {2}{B}{B}. ({2}{B}{B}, 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.)

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.)