msem-instigator

When Slyten Analyst enters, you may search your library for a card, then shuffle and put that card on top. If you do, you lose 2 life.

When Skittering Atrocity enters, up to one target creature gets -X/-X until end of turn, where X is the number of Horrors you control.

[+1]: Remove all counters from target permanent.
[+1]: Each opponent discards a card.
[–2]: Exile target creature or planeswalker card from your graveyard with mana value less than or equal to the number of lands you control. If you do, create a token that's a copy of it.
[–7]: Each opponent gets an emblem with “At the beginning of your upkeep, you lose 7 life unless you sacrifice seven permanents.”

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

Each player chooses a nonbasic card name, then searches each of their opponents' graveyards, hands, and libraries for any number of cards with the chosen name and exiles them. Each player shuffles, then draws a card for each card exiled from their hand this way.

When P-3 Ambusher enters, you may sacrifice a creature or discard a creature card. If you do, draw a card.

When Outside the Airlock enters, create a tapped 3/2 green Horror creature token.
Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life.

Deathtouch
Whenever Operative SCARY attacks or you cast a green or white spell, you may draw a card. If you do, you lose 2 life.

Search your library for a creature or sorcery card, put it into your graveyard, then shuffle.
Reconstruct {2}{B} (You may cast this from your graveyard for its reconstruct cost reduced by the mana value of a permanent you sacrifice as you cast it this way. Then exile this.)

Lost Explorer has first strike as long as it's attacking.
{1}{B}, Exile Lost Explorer from your graveyard: Crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)

Return target creature card from your graveyard to your hand. If you cast Lift Weary Heads from Rest from the graveyard, put it onto the battlefield instead.
Reconstruct {6}{B}{B} (You may cast this from your graveyard for its reconstruct cost reduced by the mana value of a permanent you sacrifice as you cast it this way. Then exile this.)

When Kill This Love enters, target opponent sacrifices a creature.
At the beginning of each end step, if a creature died this turn, you gain 2 life.

When Herald of Darkness enters, destroy up to one target creature with mana value 3 or less.

Menace
Augmented — When Gravitational Ripper enters, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, target opponent sacrifices a creature. If they can't, they discard a card.

Target creature gets -4/-4 until end of turn.

Target player discards two cards. Then exile that player's graveyard.

Trample
When Ghastly Progenitor enters, each opponent reveals their hand. Choose two nonland cards revealed this way. Their owners discard those cards.

Whenever Fleshwarper or another Horror you control dies, each opponent loses 1 life and you gain 1 life. You may mill a card.

Whenever you cast a black spell, put a +1/+1 counter on Flenser's Lieutenant.
{B}{B}: Return Flenser's Lieutenant from your graveyard to your hand.

As Extinction Specialist enters, note two creature types.
Whenever Extinction Specialist enters or attacks, choose one of the noted creature types. Creatures you don't control of the chosen type get -1/-1 until end of turn.

Choose a color. Target player reveals their hand and you choose a card of that color from it. If you do, that player discards that card and you lose 1 life.

Each player sacrifices a creature.
Reconstruct {5}{B}{B}{B} (You may cast this from your graveyard for its reconstruct cost reduced by the mana value of a permanent you sacrifice as you cast it this way. Then exile this.)

Deathtouch
When Doomed Explorer dies, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Doom deals 3 damage to any target and you gain 3 life.
Reconstruct {3}{B}{B} (You may cast this from your graveyard for its reconstruct cost reduced by the mana value of a permanent you sacrifice as you cast it this way. Then exile this.)
You may cast Doom from exile by paying {4}{B}{B}{B} rather than its mana cost. If you do, shuffle it into your library instead of putting it anywhere else as it resolves.

Desperate Android enters tapped.
Whenever another artifact you control dies for the first time each turn, return Desperate Android from your graveyard to your hand.