msem-instigator

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Sagi's Revenant deals combat damage to a player, that player discards a card.
Whenever an opponent discards a land card, you may have target creature get -2/-2 until end of turn.

Menace
Cycling {R} ({R}, Discard this card: Draw a card.)

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.

Menace
When this creature enters, put a -1/-1 counter on a creature you control.

Advance {5}{B}{B} (Cast this for {5}{B}{B} to advance it as it enters. {5}{B}{B}: Advance this as a sorcery.)
Whenever Sluiceway Collector advances, put a permanent card from a graveyard onto the battlefield under your control.

Enspirit (As you cast this spell, you may exile a nonenchantment creature you control until this leaves the battlefield or fails to resolve. Reduce this spell's cost by the exiled card's mana value.)
Haste

Flying, trample
Whenever an opponent casts a noncreature spell, that player loses 5 life unless they sacrifice a creature or discard a card.

When Terror of the Ontarachie enters, choose one —
• Each player sacrifices a creature.
• Each player loses 5 life.

Flying, lifelink
Whenever you gain life, each opponent loses 1 life.
{4}{B}{B}: Create a 1/1 black Vampire creature token with lifelink for each nontoken creature that died this turn.

Armed — Whenever Beragnian Intimidator attacks, if it's equipped, target creature can't block this turn.

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

Haste
Augmented — Whenever you cast a spell, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, put a +1/+1 counter on Bolstered Guardian. It loses this ability and gains “Whenever this attacks, it deals 2 damage to each of up to two targets.”

{2}{R}: Target creature can't block Brimstone Courser this turn.
Ride {3}{R}{R} ({3}{R}{R}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

Defender, trample
As long as you control a creature with power greater than its base power, Chained Minotaur can attack as though it didn't have defender.

Erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)
Chaosphere Ravager attacks each combat if able.

When Zwurg enters, you may discard your hand. If you do, draw X cards and add X {R}, where X is the number of different sources that dealt damage to an opponent this turn.

Flying
When Djinn of the Twisted Wish enters, it deals 5 damage to up to one target creature or battle.

Reach
Whenever a creature dealt damage by Domineering Champion this turn dies, create a 1/1 white Human creature token.

At the beginning of combat on your turn, create a 1/1 red Nomad creature token with haste.
At the beginning of your upkeep, if you control five or more creatures, you may transform Emerabi and Sunnula.

Reach, menace

{R/G}: Fento, Nova Crusader gains haste and trample until end of turn.
Whenever Fento, Nova Crusader attacks, you may put a creature card from your hand onto the battlefield tapped and attacking. If you do, sacrifice that creature at the beginning of the next end step.

Creatures you control can't be blocked by creature tokens and/or creatures with defender.
At the beginning of your end step, if Garrison Intruder didn't attack this turn, transform it.

When Helicos Aberration enters, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Hurtling Swine attacks each combat if able.

Flying
Other Dragons you control have haste.
{R}: Dragons you control get +1/+0 until end of turn.