msem-instigator

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Lord of Swarms enters or dies, target creature gets -2/-2 until end of turn.

When Lotus-Scarred Luocha enters, create a 2/1 black Spirit creature token with “This creature can't block.”
Whenever a creature in Lotus-Scarred Luocha's pack dies, each opponent loses 2 life and you gain 2 life. (Two or more creatures you control with equal power are in a pack.)

Sacrifice a creature: Put a +1/+1 counter on Masked Assailant. It gains menace until end of turn. Activate only as a sorcery.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mercenary Coercer deals combat damage to a player, that player discards a card.

Whenever you cast a spell from exile, put two +1/+1 counters on Midnight Vagrant. It gains menace until end of turn.
{1}{B}{B}: Exile the top card of target opponent's library. You may play that card during any turn you attacked with a Rogue, and you may spend mana as though it were mana of any color to cast it. Activate only as a sorcery.

Monstrous Amalgam gets +X/+X, where X is the number of creature cards in your graveyard.
{B}, Reappropriate: Put a +1/+1 counter on Monstrous Amalgam. Activate only once each turn. (To reappropriate, exile exactly two cards from your hand and/or graveyard.)

Whenever a creature dies, put a +1/+1 counter on Mother's Disciples.

Sacrifice a creature or discard a card: Exile the top card of target player's library. You may cast that card for as long as it remains exiled. Any player may activate this ability but only once each turn and only during their turn.
You and permanents you control have hexproof from spells that were exiled with Mr. Jackston or that share a name with a card exiled with Mr. Jackston.

{1}{B}, Sacrifice another creature: Put a +1/+1 counter on Nemesis Eidolon. Draw a card. Activate only as a sorcery.

Deathtouch
When Neophyte of the Old Gods enters, rediscover a sorcery card. (Look at the top card of your library. You may reveal it and put it into your hand if it's a sorcery card. Otherwise, put it back or into your graveyard.)

Deception {1}{B} ({1}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Nightfall Infiltrator deals combat damage to a player, that player discards a card.

Other Rogues you control have menace.
{2}{U}: Target blocking creature gets -1/-0 until end of turn.

Whenever a creature dies, its controller loses 1 life.

Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)
{1}{G}: Nightshade Slayer gets +2/+2 until end of turn. Activate only once each turn.

Flying, deathtouch

Other creatures you control get +2/+0.
Creatures your opponents control get -1/-1.
Fleeting {2}{B} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

When Paleolizard enters, you may discard a card. When you do, return target card from your graveyard to your hand that shares a type with that card.

When Paleontologist enters, search your library for up to two artifact and/or Skeleton cards and put them into your graveyard, then shuffle.

When Pestilent Vermin enters, target opponent loses 2 life unless they discard a card.
Whenever you cast a Tale, you may return Pestilent Vermin from your graveyard to your hand.

Ward—Discard a card. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player discards a card.)
You have “Ward—Discard a card.”

Lifelink
Whenever you gain life, each opponent loses 1 life.

When Polluted Servant enters, target opponent loses 1 life and you gain 1 life.
{2}{U}: Exile Polluted Servant, then return it to the battlefield tapped under your control.

Predatory Abomination has deathtouch and lifelink as long as you control another Horror.

Profane Emissary gets +2/+2 and has lifelink as long as you control a Demon.
If you would draw a card, you may instead search your library for a Demon card, reveal it, put it into your hand, then shuffle. You lose life equal to that card's mana value.