msem-instigator

Menace, haste
Invocation — Whenever you spend four or more mana to cast a spell or activate an ability during your turn, return Deathless Butcher from your graveyard to your hand.

Reprise {4}{U} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Target player mills a card. Create X tapped 2/2 black Zombie Pirate creature tokens, where X is the total number of cards milled by this spell.

Royster Hounds can't be blocked by creatures with power 2 or less.

When Blessed Bladewright enters, create a Weapon token. (It's an Equipment artifact with “Equipped creature gets +1/+1” and equip {2}.)
Whenever an Equipment token you control enters, attach it to up to one target creature you control.

{T}: Add {C}.
{3}{R}: Until end of turn, Defect's Precinct becomes a 3/3 creature. It's still a land. It has trample if {G} was spent to activate this ability, has vigilance if {W} was spent, and has hexproof if {U} was spent.

Humble Bridge enters tapped.
{T}: Add {R} or {W}.
When Humble Bridge enters, you may put a loyalty counter on a planeswalker you control.

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.

Flying, double strike
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Enchant opponent
Whenever a creature enters under enchanted player's control, that creature gets -0/-2 until end of turn unless that player pays 2 life.

Foretell {3}{B} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)
Each opponent discards three cards.

Create an X/X green Mutant creature token.
Draw a card.

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {U} or {B}.

Once each turn, when another creature dies, you may crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)
Whenever an artifact you control dies, Nihilistic Shock Trooper deals 1 damage to each opponent.

Vigilance
Whenever Karoa's Vanguard or another Knight you control enters, if an opponent controls more lands than you, you may search your library for a Plains card, reveal it, put it into your hand, then shuffle.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, target player discards a card.

When Chronic Traitor enters, each player sacrifices a creature. If Chronic Traitor's paranoia cost was paid, each player sacrifices two creatures instead.
Paranoia {2}{B}{B} (You may cast this spell for its paranoia cost when a permanent you control leaves the battlefield.)

When Seafloor Wreckage enters and when you sacrifice it, search your library for a basic land card, reveal it, put it into your hand, then shuffle.
{1}{G}, Sacrifice Seafloor Wreckage: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

{T}: Add {C}.
{5}, {T}, Sacrifice Wildkin Grove: Create three 1/1 colorless Shapeshifter creature tokens with changeling. (They're every creature type.)

Poisonous 2 (Whenever this creature deals combat damage to a player, that player gets two poison counters.)
When Sankataar Scourge dies, if it attacked this turn, target opponent gets a poison counter.

Creatures you control gain flying until end of turn if you control a creature with flying. The same is true for first strike, double strike, haste, hexproof, indestructible, lifelink, trample, vigilance, and prowess.

Create two 1/1 blue Elemental creature tokens with flying.

Vigilance, trample
Whenever another Horror you control enters, choose one —
• Destroy target artifact or enchantment.
• You gain 4 life.
• Apex Abomination fights another target creature.

Align X (Choose modes with total ★ less than or equal to X. You may choose modes multiple times.)
• ★ — Draw two cards, then discard two cards.
• ★★ — Draw three cards, then discard a card.
• ★★★★★ — You may cast a spell from your hand and from your graveyard without paying their mana costs.

Flying
When Stratusform Seraph enters, you may return target creature you control to its owner's hand.

Vigilance
{1}{G}{G}: Sahalia Dragoons gets +4/+4 until end of turn. Activate only once each turn.