msem-instigator

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

Flying
Whenever you cast a spell from your graveyard, return Unliving Swarm from your graveyard to your hand.

When Unmarked Vials enters, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
{1}, {T}: Add one mana of any color.

{6}{W}: Tap all creatures target player controls.

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Tap up to three target creatures. If this spell was kicked, those creatures don't untap during their controller's next untap step.

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.)

Counter target spell if four or more mana was spent to cast it.

Flying
When Unraveller of Mysteries enters, mill two cards.

Glitch—Sacrifice a creature. (Remove one [restriction] for each time you pay the glitch cost.)
When Unshackled Revolutionary enters, you may destroy target creature an opponent controls [with mana value 3 or less]. [You lose 3 life.]

When Unstable Orb enters, draw a card.
{3}, {T}, Sacrifice Unstable Orb: It deals 2 damage to target creature.

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.)

Whenever Unstable Vein enters or leaves the battlefield, choose one —
• Put a +1/+1 counter on each of up to two target creatures.
• Unstable Vein deals 2 damage to target creature with flying.

Menace
Unveil {3}{B}{R} ({3}{B}{R}: Transform this. Unveil only as a sorcery.)

Return target creature to its owner's hand.

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.

Flash
Deathtouch

{T}: Target attacking or blocking creature gets +1/+1 until end of turn.

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.

Unvirtuous Maestro can't be blocked except by three or more creatures.

Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)

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

Target creature gets -9/-0 until end of turn. Create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Distribute two +1/+1 counters among one or two target creatures.

Rhapsody {4}{R}{W} (Pay {4}{R}{W} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Lifelink, haste