msem-instigator

Flying, vigilance
When Tyriel, Angelic Artisan enters, you may search your library for an Equipment card, reveal it, put it into your hand, then shuffle.
Whenever Tyriel attacks, you may put an Equipment card from your hand onto the battlefield, then attach it to Tyriel.

This spell costs {1} less to cast for each Scarecrow you control.
Other creatures you control get +0/+2 and have vigilance.

Other Hounds you control have trample.
{R/W}, {T}: Put a +1/+1 counter on target Hound you control.

{2/B}: Umbral Stalker gains indestructible until end of turn. Tap it.

Resolute — Umbral Wolf can't be blocked by more than one creature as long as Umbral Wolf's power is greater than its base power.

Assault {X}{R}{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.)
Other Elementals you control get +1/+0.
When Unbound Annihilus assaults, create X 1/1 red Elemental creature tokens that are tapped and attacking.

Whenever you cast another creature spell, create a 1/1 green and white Elk Spirit creature token.
As long as you control five or more Elk, creatures you control get +3/+3 and have trample.

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

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

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.

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

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.”

Flying, vigilance
When you attain Unfallen Angel, target opponent discards a card.

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

Add X mana in any combination of colors, where X is the amount of mana spent to cast Unravel Shattered Worlds.
Coalesce {7} (You may cast this from your graveyard for {7}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Unreflected Cultist can't be blocked by Reflections.

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Unstable Borer attacks each combat if able.

Create a 2/2 white Angel creature token with flying.
Coalesce {6}{W}{W} (You may cast this from your graveyard for {6}{W}{W}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Flying

Menace

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

When Vagabones enters, look at the top two cards of your library. Put any number of them into your graveyard and the rest on top of your library in any order.

Advance {6}{W}{W} (Cast this for {6}{W}{W} to advance it as it enters. {6}{W}{W}: Advance this as a sorcery.)
Flying, vigilance, lifelink
Whenever Valera, Constructed Angel advances, destroy all nonartifact creatures.

Advance {3}{R}{W}{B} (Cast this for {3}{R}{W}{B} to advance it as it enters. {3}{R}{W}{B}: Advance this as a sorcery.)
Whenever Valinov Vandal advances, target opponent sacrifices a permanent. Put a +1/+1 counter on Valinov Vandal.