msem-instigator

Enchant creature
When Rotten Retinue enters, return target creature card from your graveyard to your hand.
Enchanted creature gets +2/+2 and has deathtouch.

Return target permanent you control to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Ifram's Cavalier enters with two additional +1/+1 counters on it if you didn't cast it from your hand.

Converge — Let It Burn enters with a charge counter on it for each color of mana spent to cast it.
{1}{R}, Remove a charge counter from Let It Burn: It deals 3 damage to any target.
When there are no charge counters on Let It Burn, return it to its owner's hand.

When Wu, the Shackled enters, you may have an opponent gain control of it. If you do, draw two cards.
At the beginning of your upkeep, if you don't own Wu, it fights another target creature you control and its owner draws a card.

Flying
When Foul Drifter enters, target creature gets -1/-1 until end of turn.

Rhapsody {3}{W}{W} (Pay {3}{W}{W} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Lifelink

Whenever one or more creatures die for the first time each turn, you draw a card and you lose 1 life.
Whenever you cast a black noncreature spell, Villainy deals 2 damage to any target and you gain 2 life.

Colossal 4—{5}{G} (You may cast this for its colossal cost to have it enter with four +1/+1 counters; or pay {5}{G} as a sorcery: Put four +1/+1 counters on it if it has none.)
Trample

When Ethersketch Blueprints enters, create a 1/1 blue Thopter artifact creature token with flying.
{2}, Sacrifice Ethersketch Blueprints: Draw a card.
Monument {5}{B}{B} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)
Ascend {4}{W} ({4}{W}: Exile this permanent, then return it to the battlefield transformed. Ascend only as a sorcery.)

Creatures you control get +2/+2 until end of turn.

Whenever you cast a spell, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
Harmony — Yita, Almgrove Prodigy gains your choice of flying, first strike, vigilance, lifelink, hexproof, or haste until end of turn.

Defender (This creature can't attack.)
Whenever you cast a spell, if it isn't your main phase, Serene Meditant loses defender until the beginning of your next end step.

When Scuripi Collector enters, return target artifact, enchantment, or land card from your graveyard to your hand.

Whenever you cast a spell from exile, copy that spell. You may choose new targets for the copy.
{B}, Discard a card: When you next cast a spell from your hand this turn, it gains rerun. Activate this ability only once each turn. (Exile it as it resolves if you cast it from your hand. Whenever a creature you control dies, you may cast that card from exile without paying its mana cost.)

Reach
Attain {4}{G} ({4}{G}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Mechanized Ideal gets +X/+Y, where X is the highest base power among other creatures you control and Y is the highest base toughness among other creatures you control.

When Bayou Courier enters, you may pay 2 life. If you do, create a 3/2 green Crocodile creature token with trample.

Create a 2/2 colorless Spirit creature token.
Draw a card.

Pressure {2}{B}{B} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
When Gloomtide Whelk enters, all other creatures get -4/-4 until end of turn.

Exile target nonland permanent. As long as it remains exiled, its owner may return it to the battlefield any time they could cast an instant. If you control that permanent, you may activate its loyalty abilities any time you could cast an instant during that turn.

When Overwhelming Paperwork enters or is put into a graveyard from the battlefield, return up to one target creature to its owner's hand.
{3}{U}{U}: Sacrifice Overwhelming Paperwork. Activate only as a sorcery.

When Raikai Seafarer enters, you may search your library for up to three cards named Raikai Seafarer, reveal them, put them into your hand, then shuffle.