msem-instigator

Kicker {X}{U} (You may pay an additional {X}{U} as you cast this spell.)
When Tidetwister Mage enters, if it was kicked, return all other creatures with power X or less to their owners' hands.

This spell costs {1} less to cast for each +1/+1 counter among creatures you control.
Hoof Cliff Heartminer enters with four +1/+1 counters on it.
Whenever Hoof Cliff Heartminer or another creature you control leaves the battlefield, you may put its +1/+1 counters on another target creature you control.

When Seishin Rageshaper enters, create a 2/2 colorless Spirit creature token.
Colorless creatures you control have haste.

When Rixia, Rift Shunted enters, target creature can't be blocked this turn.
Whenever a creature you control deals combat damage to an opponent, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

When this creature enters, put two -1/-1 counters on a creature you control.
{B}: Target creature with a counter on it gains deathtouch until end of turn.

When Warfan of Changing Winds enters, draw a card.
Whenever a card you own is exiled from anywhere, you may put it on the bottom of your library.

Enchant creature
Enchanted creature has vigilance.
When enchanted creature deals combat damage to a player, return Eternal Path to its owner's hand.

When Disassociate enters, exile target creature until Disassociate leaves the battlefield.

Flying
{1}, Sacrifice a creature: Mahara Angel gets +1/+1 until end of turn.

Tap an untapped Desert you control: Hostile Atmosphere deals 1 damage to any target.

Trample, haste
When Rejuvenating Elemental enters, remove up to X -1/-1 counters from among creatures you control. Rejuvenating Elemental gets +1/+1 until end of turn for each counter removed this way.

Whenever one or more creatures you control deal combat damage to a player or planeswalker, create a Clue token.
{G}{U}, Sacrifice a Clue: Put a +1/+1 counter on target creature. Proliferate.

Return target creature card from your graveyard to the battlefield.
Fabled {2}{B} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Reverberate {2}{U} (When you cast this spell, copy it if you paid its reverberate cost. You may choose new targets for the copy.)
Target creature gets +0/+3 and gains hexproof until end of turn.

Flash (You may cast this spell any time you could cast an instant.)
When Wind-Blessed Guardian enters, you may return target permanent you control to its owner's hand.

Flash
Cycling {2} ({2}, Discard this card: Draw a card.)

Creatures your opponents control get -1/-1 until end of turn. You gain 2 life.

At the beginning of combat on your turn, if you control a creature with power greater than its base power, Satyr Trailblazer gets +2/+0 until end of turn.

Whenever one or more creatures you control attack, create a 1/1 white Human Samurai creature token.

{W}{B}, {T}: Exile target nonland permanent until Ediam, the Inside Man leaves the battlefield. You may cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell.

You may cast spells with mana value 5 or greater as though they had flash.
As long as you control a permanent with mana value 5 or greater, Cenotaph Conjurant gets +2/+0 and can't be blocked.

Haste
When Gilded Gearhulk enters, you may destroy target noncreature, nonland permanent.

Reverberate {3}{U} (When you cast this spell, copy it if you paid its reverberate cost. You may choose new targets for the copy.)
Create a token that's a copy of target creature you control.

First strike, lifelink
Once each turn, when another nontoken creature you control dies, you may create a 2/2 white Elk Spirit creature token with first strike and lifelink named Fawn of Hesediel.

Target creature gains flying and double strike until end of turn.
Flashback {2}{U}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)