msem-instigator

Whenever Battle-Scarred Combatant attacks or blocks, put a -1/-1 counter on it.

This spell costs {2} less to cast if you've cast a blue noncreature spell this turn. The same is true for a red noncreature spell.
Menace

When Corrupt Warden enters, up to one target creature gets -X/-X until end of turn, where X is the number of card types among cards in your graveyard.

This spell costs {1} less to cast for each card type among cards in your graveyard.
Deathtouch

Deathtouch
Cutthroat Deceiver enters with four -1/-1 counters on it.
{3}{B}, {T}: Move a -1/-1 counter from Cutthroat Deceiver onto another target creature.

All creatures get -3/-2 until end of turn.
Coalesce {6}{B}{B} (You may cast this from your graveyard for {6}{B}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Haste (This creature can attack and {T} as soon as it comes under your control.)
Whenever a creature you control attacks, each opponent loses 1 life.

Indestructible
As long as your devotion to black is less than five, Erebos isn't a creature.
Other creatures you control dying causes abilities of that creature to trigger as though it entered.
{2}{B}: Each opponent loses 1 life. You gain life equal to the life lost this way.

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Cycling {B} ({B}, Discard this card: Draw a card.)

Whenever Halford enters or attacks, an opponent chooses one. When they choose one that has already been chosen, copy that ability.
• That opponent loses 2 life and you gain 2 life.
• That opponent sacrifices a permanent.
• That opponent discards a card. If they can't, draw a card.

Menace
Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 until end of turn for each creature card in your graveyard.

Flying, trample
At the beginning of your upkeep, sacrifice a creature.
Revive {2}{B}{B} ({2}{B}{B}, 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.)

Flying
Kai'Wej, the Desolate has indestructible as long as you control no other creatures.
{1}{B}{B}, Sacrifice two creatures: Return Kai'Wej from your graveyard to the battlefield tapped.

Flying, lifelink
Other Demons you control have flying and lifelink.
If you would create a creature token, you may instead pay 5 life and create a 5/5 black Demon creature token.

Flying, trample
When Lord of Sacrilege enters, each opponent loses 3 life, discards a card, then sacrifices a nonland permanent. If you control three or more Demons and/or Warlocks, instead each opponent loses 6 life, discards two cards, then sacrifices two nonland permanents.

This spell costs {1} less to cast if you control a Warrior.

Play with the top card of your library revealed.
Whenever you draw a card, destroy each creature with the same mana value as that card.

Menace
Sabotage — Whenever an opponent or permanent an opponent controls becomes the target of a spell you control, each opponent discards a card.

Deathtouch
When Scion of Desolation enters, put target creature card with mana value 3 or less from a graveyard onto the battlefield under your control.
Whenever a Swamp you control enters, you may aetherize Scion of Desolation. (To aetherize, create a token that's a copy of it, then exile that token.)

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.)
Menace

First mate — Each nonland card in your starting deck is an artifact, a Pirate, or has “artifact,” “Treasure,” or “Pirate” in its printed rules text. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Whenever Tinbeard of the Brine attacks, each opponent loses X life and you gain X life, where X is the number of artifacts you control plus the number of Pirates you control.

Menace
Titan of Fallen Stars gets +1/+1 from -1/-1 counters instead of -1/-1.
When Titan of Fallen Stars enters, move any number of -1/-1 counters from creatures you control onto Titan of Fallen Stars.

Flying
{2}{B}, Sacrifice another creature: Target creature gets -3/-3 until end of turn.

Haste
Disgraced 1 (This enters with a -1/-1 counter. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)

When Ageless Ascetic enters, return up to one target instant or sorcery card from your graveyard to your hand.