msem-instigator

When Beyond the Veil enters, another target nonland permanent phases out. (Treat it and anything attached to it as though they don't exist.)
Permanents you don't control with mana value 3 or less can't phase in.

Once each turn, when Atal, the Shroudmaker enters or you attack with one or more Horrors, you may create two tapped 1/1 colorless Human creature tokens. If Atal isn't a token, creatures you control gain flying until end of turn.
{2}{W}{W}, Discard Atal: Create a token that's a copy of Atal, the Shroudmaker, except it's 4/4 and isn't legendary. Activate only as a sorcery.

Exile target creature. At the beginning of the next end step, return that card to the battlefield under its owner's control with your choice of X counters on it from among +1/+1, flying, first strike, lifelink, or vigilance.

Shroudmaker's Domain enters tapped.
{T}: Add {W}.

{1}, Sacrifice Aberrant Apostle: Choose one. This ability costs {1} less to activate as long as Aberrant Apostle entered this turn.
• Destroy target artifact.
• Destroy target enchantment.
• Exile target card from a graveyard.

Flying, trample
Once during each of your turns, you may cast a spell from your graveyard without paying its mana cost.
When Yhzag, Alpha and Omega is put into a graveyard from anywhere, its owner shuffles their graveyard into their library.

You may cast What Remains of Samuel Quinn from your graveyard and from the battlefield. It costs {G}{G} more to cast this way.
What Remains of Samuel Quinn enters with your choice of X counters from among +1/+1, vigilance, reach, and trample.

When Screams from the Deep enters, exile up to one target monocolored permanent.
As long as an opponent owns three or more cards in exile, you may have Screams from the Deep assign its combat damage as though it weren't blocked.
Evoke {5} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Flying, vigilance
When Formless Eidolon enters, create a tapped token that's a copy of target land you control.
Evoke {3} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Sunken Homestead enters tapped.
{T}: Add {B}.
{2}{B}: Until end of turn, Sunken Homestead becomes a 2/2 Zombie creature with “When this creature dies, return it to the battlefield.” Activate only if you're horrific.

Misty Churchyard enters tapped.
{T}: Add {W}.
{1}{W}{W}: Until end of turn, Misty Churchyard becomes a 1/4 Cleric creature with “Whenever this creature is dealt damage, put that many +1/+1 counters on it.” Activate only if you're horrific.

Lost Station enters tapped.
{T}: Add {U}.
{U}{U}: Until end of turn, Lost Station becomes a 2/2 Horror creature with “This creature can't be blocked.” Activate only if you're horrific.

Hellfire Caverns enters tapped.
{T}: Add {R}.
{2}{R}: Until end of turn, Hellfire Caverns becomes a 3/3 Devil creature with menace. Activate only if you're horrific.

Enshrouded Village enters tapped.
{T}: Add {G}.
{1}{G}{G}: Until end of turn, Enshrouded Village becomes a 4/4 Human creature with trample. Activate only if you're horrific.

Menace
Discard a creature card or sacrifice a creature or exile a creature card from your graveyard: Put a +1/+1 counter on Starving Stalker. Activate only once each turn.

Trample
When The Shepherd of Nowhere enters, each player sacrifices each other nontoken creature they control.
Whenever another nontoken creature you control dies, create a token that's a copy of that creature.

This spell costs {2} less to cast for each creature that died this turn.
Each player exiles all creature cards from their graveyard, then sacrifices each creature they control, then puts all creature cards they own exiled this way onto the battlefield. Exile Sea of Corpses.

Ravenous Attraction enters with a +1/+1 counter on it.
Whenever a creature you control dies, double the number of each kind of counter on Ravenous Attraction.

You may have Raging Reflection enter as a copy of any creature on the battlefield, except it has “When this creature enters, it fights another target creature that shares a name with it.”

Whenever you tap a land for mana, add one mana of any type that land produced.
Whenever you cast a spell with mana value greater than the number of lands you control, sacrifice a land.

Whenever Morbid Mimic enters or attacks, exile up to one target creature card from a graveyard.
Morbid Mimic has all activated abilities of cards exiled with it.

Whenever you cast a spell from exile, copy that spell. You may choose new targets for the copy.
{B}, Discard a card: When you next cast a spell from your hand this turn, it gains rerun. Activate this ability only once each turn. (Exile it as it resolves if you cast it from your hand. Whenever a creature you control dies, you may cast that card from exile without paying its mana cost.)

If another creature you control would die, exile it instead.
When John Furo, the Unfortunate dies, until your next end step, you may play cards exiled with John Furo.

First strike
Noncreature spells cost {1} more to cast as long as their controller is horrific. (A player is horrific as long as they've sacrificed a permanent or discarded a card this turn.)

Zealous Rabble gets +1/+1 for each creature token you control.
At the beginning of your end step, if you're horrific, create a token that's a copy of Zealous Rabble, except it doesn't have this ability. (You're horrific as long as you've sacrificed a permanent or discarded a card this turn.)