msem-instigator

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

Whenever you copy an instant or sorcery spell, you may pay {1}{U}. If you do, draw a card.
Whenever you cast an instant or sorcery spell, you may pay {1}{R}. If you do, Unbound Researchers deals 2 damage to target player or planeswalker.

Unbound Spirit can't be blocked.
When you attain Unbound Spirit, tap target creature. That creature doesn't untap during its controller's next untap step.

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.

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.)

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

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.

Trample
Defiance (Whenever this creature takes damage, if it survives and wasn't defiant, put a +1/+1 counter on it and it becomes defiant.)

Flying
When Unraveller of Mysteries enters, mill two cards.

Unreflected Cultist can't be blocked by Reflections.

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever Unruly Magus deals combat damage to a player, draw a card.

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

Rhapsody {4}{U}{U} (Pay {4}{U}{U} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
When Unstable Prophet enters, surveil X, where X is its power. (Look at the top X cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

When Unwavering Sentinel enters, for each creature you control, create a white Aura enchantment token named Shield with “Enchant creature” and “If enchanted creature would be destroyed, instead remove all damage from it and sacrifice this Aura” attached to that creature.

Disgraced 1 (This enters with a -1/-1 counter. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)
Attain {3}{W} ({3}{W}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

At the beginning of each combat, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
Harmony — Target creature gets +1/+1 and your choice of flying, haste, or vigilance until end of turn.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
When Ushi Yun enters, create an Idol token.
As long as you're in a renaissance, artifacts you control have “{T}: Draw a card.”

Flash
Death knell — Put a +1/+1 counter on each creature you control. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

Other legendary creatures you control get +1/+1.
At the beginning of your upkeep, you may search your library for a legendary card, reveal that card, and put it into your hand. If you do, you skip your draw step this turn and shuffle.

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.

As long as an opponent has one or fewer cards in hand, Valdez gets +2/+0 and has menace.

Whenever Valinov Collector or another artifact you control enters, Valinov Collector deals 2 damage to each opponent and you gain 2 life.

Advance {4}{B}{B} (Cast this for {4}{B}{B} to advance it as it enters. {4}{B}{B}: Advance this as a sorcery.)
Flying
Whenever Valinov Siphoner advances, target player loses 2 life and you gain 2 life.

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.

Flying
Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)