msem-instigator

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.

Menace, haste
Invocation — Whenever you spend four or more mana to cast a spell or activate an ability during your turn, return Deathless Butcher from your graveyard to your hand.

When Dread Elk dies, put a +1/+1 counter on target creature you control. If that creature is a Zombie, put two +1/+1 counters on it instead.
Foreshadow {5}{B} (You may cast this spell for its foreshadow cost. If you do, also trigger its “dies” abilities when it enters.)

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.

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

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{2}{B}, Discard a card: Mercenary of the Folded Fan gains indestructible until end of turn. Tap it. If you're in a renaissance, draw a card.

Trample, haste
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)
At the beginning of your end step, sacrifice a creature.

When Mukal Swarmhorde enters, put a +1/+1 counter on each other Construct you control.
Respawn (When this creature dies, if it attacked this turn, return it to its owner's hand.)

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
At the beginning of your end step, if an opponent is cursed, surveil 2.

Lifelink
When this creature enters, it seeks secrets. (Give it that Oath Aura. Fulfill it by attacking with it and two or more other creatures to draw a card.)