msem-instigator

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

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

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.

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.

At the beginning of your upkeep, you may create a Treasure token. If you do, an opponent of your choice creates a tapped Treasure token.

Target creature can't block until end of turn. If that creature had a Steed attached to it, unattach that Steed and it can't block until end of turn.
Draw a card.

Exile the top five cards of your library. Until end of turn, you may play any number of cards exiled this way with mana value less than or equal to the number of colors among permanents you controlled as you cast United Fervor.

Unleash the Dragon deals 1 damage to any target for each spell cast this turn.

Target creature you control gains erratic until end of turn. You may have it fight another target creature. (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)

This spell costs {2} less to cast if your starting deck contained at least forty cards more than the minimum deck size.
When Unrivaled Fireweaver enters, you may exile a red instant or sorcery card you own from outside the game. Until the end of your next turn, you may play that card.

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

Target attacking creature fights another target attacking creature.

You may have Unstable Impersonator enter as a copy of any creature on the battlefield chosen at random.

Vanishing 5 (This creature enters with five time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
{1}{R}, Remove a time counter from Unstable Magmaling: Flip a coin. If you win the flip, it deals 3 damage to any target.

Unstoppable Slaughter deals 1 damage to each creature and each player. Whenever a creature dealt damage by Unstoppable Slaughter this turn dies this turn, repeat that process.

Target creature you control gets +1/+0 until end of turn. That creature deals damage equal to its power to another target creature.

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
Whenever a creature you control becomes renowned, create a 1/1 red Soldier creature token with haste.

Target attacking creature gets +1/+0 until end of turn. When that creature dies this turn, it deals damage equal to its power to defending player.

Menace (This creature can't be blocked except by two or more creatures.)
Engage (This creature must be blocked each combat if able.)

Gain control of target creature until end of turn. Untap that creature. It gains haste and is marked until end of turn.

Haste
When Urud Stingswoop enters, it gains flying until end of turn.

Assault {1}{R} (Whenever this attacks, if it has no +1/+1 counters on it, you may pay its assault cost to put a +1/+1 counter on it.)
When Urudi Warlord assaults, it gains first strike until end of turn.

Exile all lands. For each land card exiled this way, Uttermost Obliteration deals 1 damage to that land's controller.