msem-instigator

Once each turn, when Groz, the Nightshaper enters or you attack with one or more Horrors, you may return target nonlegendary creature card from your graveyard to your hand. Then if Groz isn't a token, create a token that's a copy of that creature card.
{2}{B}{B}, Discard Groz: Create a token that's a copy of Groz, the Nightshaper, except it's 4/4 and isn't legendary. Activate only as a sorcery.

Marrowskitter can't block and can't be blocked.
{3}{B}{B}: Return Marrowskitter from your graveyard to the battlefield. Create a token that's a copy of it.

Rattlecage Terror enters tapped.
{1}{B}: Return Rattlecage Terror from your graveyard to your hand. When you do, another target creature card with mana value 3 or less in your graveyard gains this activated ability until end of turn, except it costs {1} more to activate.

Destroy target creature with mana value 2 or less. If it was a token, you gain 2 life.

Target player mills a card. Create a 3/2 colorless Horror creature token. Put a decayed counter on it. (It can't block. When it attacks, sacrifice it at end of combat.)

Once each turn, when you cast a noncreature spell, create a 1/1 colorless Human creature token. Put a prowess counter on it.

[+1]: Creatures you control get +1/+0 and gain haste until end of turn.
[0]: Bennett Brooks deals 2 damage to each opponent. If you have an insight counter, create two Treasure tokens.
[0]: You get an insight counter.
[–2]: Sacrifice an artifact. If you do, return target artifact card from your graveyard to the battlefield.

Blazing Exultation deals 3 damage to any target.
{2}{R}: Shuffle Blazing Exultation and up to one other instant or sorcery card from your graveyard into your library.

Flying, menace, haste
When Bloodfiend Ravager enters, it deals 2 damage to any target. If a permanent dealt damage this way would die this turn, exile it instead.
Evoke {1}{R} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Menace
Sacrifice another creature: Corpulent Gibberer deals 1 damage to any target.
Evoke {1}{R} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead, except the additional tokens are named Ingenious Idea.
At the beginning of your end step, exile each token you control named Ingenious Idea.

Enchant creature
Enchanted creature gets +1/+0 and has menace and haste.
You may cast Empty the Magazine from your graveyard by paying {3}{R} rather than paying its mana cost.

Once each turn, when Eruq, the Flamebearer enters or you attack with one or more Horrors, you may have Eruq deal 2 damage to each opponent. Then if Eruq isn't a token, gain control of target creature an opponent controls until end of turn. Tap it. It's attacking its controller.
{2}{R}{R}, Discard Eruq: Create a token that's a copy of Eruq, the Flamebearer, except it's 4/4 and isn't legendary. Activate only as a sorcery.

Choose one. If you attacked with a creature with mana value 5 or greater this turn, you may choose any number instead.
• Destroy target artifact.
• Destroy target land.
• Fate of the World deals 3 damage divided as you choose among one, two, or three targets.

Menace
Whenever an opponent activates an ability that isn't a mana ability, Flensing Tormentor deals 1 damage to that player.

Flamebearer's Domain enters tapped.
{T}: Add {R}.

{T}: Keepers of the Reach deals 1 damage to each opponent.
{2}{R}, {T}: Keepers of the Reach deals 3 damage to each opponent. Activate only if you control a permanent with mana value 5 or greater.

When Mouthpiece of Yhzag enters, you may have target opponent create a tapped 1/1 colorless Human creature token.
Whenever Mouthpiece of Yhzag attacks, gain control of target Human creature you don't control with mana value 3 or less until end of turn. Tap it. It's attacking.

At the beginning of your upkeep, Reality Collapse deals 1 damage to each opponent.
{2}{R}: Until end of turn, whenever an opponent is dealt noncombat damage, Reality Collapse deals that much damage to target creature that player controls.

{T}: Target creature gains haste until end of turn.
{1}{R}, {T}, Sacrifice a Human: Create a token that's a copy of the sacrificed creature, except it's a 3/2 colorless Horror. It gains haste until end of turn. Activate only as a sorcery.

If you would draw a card, you may skip that draw. If you do, create a tapped Treasure token and exile the top card of your library. You may play that card this turn.

Flying
{1}{R}{R}{R}: Return Umbral Hunter from your graveyard to your hand. If it's the declare attackers step, up to one target attacking creature gets +3/+1 until end of turn.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Once each turn, when one or more counters are put on a permanent you control, create a 1/1 colorless Human creature token.
Whenever you attack with three or more creatures, destroy up to one target artifact or enchantment.

Reach, vigilance
When Amorphous Tyrant enters, another target creature you control deals damage equal to its power to target creature or planeswalker you don't control.
Evoke {G} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

[+1]: Add two mana of any one color.
[0]: Put two +1/+1 counters on target creature you control. Then put your choice of a reach, vigilance, or trample counter on it. If you have an insight counter, you may put all of those counters on that creature instead.
[0]: You get an insight counter.
[–2]: Destroy target noncreature, nonland permanent.