msem-instigator

Whenever a creature you control becomes blocked, you may return it to its owner's hand.
The first spell you cast during your postcombat main phase each turn costs {W}{U} less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a spell with mana cost {1}{U}, it costs {1} to cast.)

Flying
When Tattered Wisp enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Flying, protection from Dragons

When Abomination Broodmother dies, create a 3/2 green Horror creature token.

As an additional cost to cast this spell, exile two permanent cards from your graveyard.
You may cast Adiran Survivors from your graveyard.

Haste
Whenever Arisen Hunter attacks, target player loses 2 life and you gain 2 life.
If Arisen Hunter would die, exile it instead.

When Augmented Alchemist enters or dies, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

When Blightbringer enters, creatures your opponents control get -1/-1 until end of turn.
Unearth {3}{B} ({3}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

Disgraced 1 (This enters with a -1/-1 counter. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)
At the beginning of each player's upkeep, put a -1/-1 counter on target creature that player controls.

Pressure—{B}, Exile six cards from your graveyard. (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Deathtouch
{B}, Exile six cards from your graveyard: Return Danithra Champion from your graveyard to the battlefield. Activate only during your turn.

Lifelink
Vanishing 1 (This creature enters with a time counter on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever another creature you control dies, put a time counter on Dulling Necromancer.

Flying, deathtouch
{B}: Emissary of Dreaded Night gets +1/+1 until end of turn. Activate only if Emissary of Dreaded Night is embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

When Felhide Marauder enters, if you control a creature with power greater than its base power, Felhide Marauder gains haste until end of turn.

Menace
When Fenhauler Gang enters, each player mills three cards.
Whenever Fenhauler Gang deals combat damage to a player, return up to one target creature or land card from your graveyard to your hand.

Flying
When Fickle Songstress enters, target opponent gains control of it.
Whenever you lose life, if you don't own Fickle Songstress, its owner gains control of it.

Flash

Menace
When Graygulch Outcast dies, each opponent loses 3 life.

Pressure {2}{B} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Menace (This creature can't be blocked except by two or more creatures.)

At the beginning of each opponent's end step, that player loses 1 life for each creature they control unless they sacrifice a creature. Then they lose 1 life for each card in their hand unless they discard a card.

Whenever a creature you control dies, Insidious Terror gets +1/+0 and gains menace until end of 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.)
When Kantra of Avarice enters, target player draws two cards and loses 2 life.

Whenever a creature an opponent controls dies, that player loses 1 life.
At the beginning of your end step, if an opponent lost 3 or more life this turn, create a 1/1 white Human creature token.
Fleeting {B} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Lifelink
When Leyran-Pack Outcast attacks, if it's alpha, each player sacrifices a creature.

Menace
Landfall — Whenever a land you control enters, Mawdryk's Elite gets +1/+0 and gains deathtouch until end of turn.

Menace