msem-instigator

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
If you would gain life, you may put a +1/+1 counter on this creature instead.
When this creature has toughness 20 or greater, you win the game.

This spell costs {2} less to cast for each Horror you control.
Exile up to one target non-Horror creature.
Coalesce {8}{W} (You may cast this from your graveyard for {8}{W}. If you do, put it onto the battlefield as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
Lifelink

Create a 2/2 white Angel creature token with flying.
Coalesce {6}{W}{W} (You may cast this from your graveyard for its coalesce cost. If you do, put it onto the battlefield as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Flying

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
If this creature would die, you may instead put a card or token merged with it into its owner's graveyard. If you do, remove all damage marked on this creature.

Once each turn, you may activate an additional loyalty ability of a planeswalker you control.
[+1]: You gain 1 life for each loyalty ability you've activated this turn. Scry 1.
[0]: Put a +1/+1 counter on target creature. It can't attack or block until your next turn.
[–3]: Exile target creature with power 4 or greater.

Destroy all non-Horror creatures.
Coalesce {8}{W}{W} (You may cast this from your graveyard for its coalesce cost. If you do, put it onto the battlefield as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

When Bearer of Silk Chains enters the battlefield, gain control of target nonland permanent until Bearer of Silk Chains leaves the battlefield. If that permanent is a Horror, gain control of it instead.

Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Whenever you draw a card, you may exile the top card of your library.
{3}{U}{U}, Sacrifice Collector of Memories: Shuffle your hand into your library, then put each card exiled with Collector of Memories into its owner's hand.

Whenever an opponent casts a spell, that player gets a poison counter unless they pay {1}.
As long as an opponent has five or more poison counters, Corrupted Soothsayer gets +2/+1 and has flying.

Counter target spell with mana value 3 or less.

This spell can't be countered.
Tap up to three target permanents.
Coalesce {9}{U}{U} (You may cast this from your graveyard for its coalesce cost. If you do, put it onto the battlefield as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Opponents can't untap more than two permanents during their untap steps while Drown Amidst the Cosmos is on the battlefield.

Flash
{U}, Put Elusive Hunter into its owner's library second from the top: Counter up to one target spell unless its controller pays {2}.

Target player shuffles up to three target cards from their graveyard into their library.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Whenever you draw your second card each turn, put a +1/+1 counter on Ethereal Sneak.

Search target opponent's library for a nonland card. You may cast that card without paying its mana cost. Then that player shuffles.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Whenever you draw your second card each turn, draw a card.

This spell costs {2} less to cast if its target's controller is poisoned.
Counter target spell unless its controller pays {X}.

You may reveal a Revelation card you own from outside the game or choose a face-up Revelation card you own in exile. Put that card into your hand. Exile From Stars Above.

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.
Untap each Horror you control during enchanted creature's controller's untap step.

Flying
When Helar Ritualist enters the battlefield or whenever you cast a spell, if {W}{B} was spent to cast it, each opponent loses 3 life and you gain 3 life. Put a +1/+1 counter on Helar Ritualist.

The next time you cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Create a 1/1 blue Illusion creature token with “This gets +1/+1 for each other Illusion you control.”
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Defender
When Mnemonic Wall enters the battlefield, you may return target instant or sorcery card from your graveyard to your hand.