msem-instigator

When Debaser of Truth enters, if you control three or more Horrors, each opponent discards two cards.
Other Horror creatures you control get +1/+1.

Whenever Defective Abomination attacks, you may sacrifice a permanent. If you do, put a +1/+1 counter on it. It gains indestructible until end of turn.

Whenever you scry, tap target creature an opponent controls.
{2}{W}{U}: Scry 1. You gain 1 life.

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Each creature you control with a counter on it has ward {2}. (If a creature has multiple instances of ward, each triggers separately.)

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
When Demolitionist Deviser dies, it deals damage equal to its power to any target.

Create three 1/1 colorless Servo artifact creature tokens.

Counter target nonenchantment spell.

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.

Target creature you control deals damage equal to its power to target creature or planeswalker you don't control. Scry 1.

{2}, {T}: Exile target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step. Activate only as a sorcery.

Flying, haste
{2}{B}: Devourer of Dread gets +1/+1 until end of turn. If there are three or more creature cards in your graveyard, put a +1/+1 counter on Devourer of Dread instead.

You may cast spells as though they had flash.
Whenever you cast a sorcery spell, each opponent loses 3 life unless they discard a card or sacrifice a nonland permanent.

Flying
Ward—Pay 2 life. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 2 life.)
Whenever Dire Harpies of Odunos or another creature with flying you control enters, each opponent loses 1 life and you gain 1 life.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Until your next turn, up to one target creature can't attack or block and its activated abilities can't be activated.
[Lore III] Target opponent skips their next combat phase.

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.

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

At the beginning of your first main phase, add {R}.
Whenever a colossal ability puts one or more counters on a creature you control, Draconic Symphony deals 2 damage to any target.

Whenever an artifact you control is put into a graveyard from the battlefield, create a 4/4 red Dragon creature token with flying.

When Drown in Apathy enters, exile target creature until Drown in Apathy leaves the battlefield. If a permanent would be returned to the battlefield this way, put it in its owner's hand instead.

All creatures get -2/-2 until end of turn. Scry 1.

Creatures you control enter with a +1/+1 counter on them if you spend three or more colors of mana to cast them.

When Earthbreaker Behemoth enters, it deals damage equal to its power to up to one target creature you don't control. Excess damage is dealt to that creature's controller instead.

Return up to six target cards in your graveyard that don't share colors to your hand.
Exile Earthly Ambitions.

Enchant creature
Enchanted creature has “Whenever this creature deals combat damage to a player, create a token that's a copy of it, except it's a 1/1 Reflection” and “When this creature leaves the battlefield, sacrifice all Reflections you control.”

Your opponents can't gain life.
Whenever you cast a noncreature spell, put a +1/+1 counter on Eidolon of the Arena.