msem-instigator

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, put a +1/+1 counter on Mei's Collector.

Indestructible
When Reflected Worldwalker enters, each player puts their hand into their sideboard.

Target creature gets -1/-1 until end of turn. Create a 1/1 green Saproling creature token.

Choose one —
• Tap target creature.
• Untap target creature and remove it from combat.
Draw a card.

Harness (You may tap a creature you control as you cast this spell. If you do, reduce that spell's mana cost by that creature's power.)
When Darutu's Plow enters, if it was harnessed by an Ox, untap that Ox and attach Darutu's Plow to it.
Equipped creature gets +0/+2 and assigns combat damage equal to its toughness rather than its power.
Equip {3}

Counter target spell.
Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Target player sacrifices a creature. Fateseal 1. (To fateseal 1, look at the top card of an opponent's library, then you may put it on the bottom of that player's library.)

Create a token that's a copy of target permanent you control, except it isn't legendary. Then put Picture Perfect on the bottom of its owner's library if you cast it from exile.
Leitmotif (If you cast this spell from your hand, exile it as it resolves. When you next cast a spell that shares a color with this card, you may cast this from exile without paying its mana cost.)

Skysworn Aspirant has flying as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 and gains menace until end of turn.

When Bug Catcher enters, create a 1/1 green Insect creature token.
Whenever a nontoken Insect you control dies, create a 1/1 green Insect creature token.

Vigilance
Seawise Swain gets +1/+1 as long as you control an artifact.
Seawise Swain gets +1/+1 as long as you control an enchantment.

If a creature entering the battlefield under your control causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
{1}{U}, {T}: Exile another target creature. Return it to the battlefield under its owner's control at the beginning of the next end step.

When Warden of Rehis-Dorahn enters, put a -1/-1 counter on each creature.
{2}{B}{G}, {T}: Destroy target creature with a counter on it.

As long as it's your turn, Shell Merc has first strike and prowess.

Flying
Whenever Rivha and at least two other creatures attack, exile all other attacking creatures you control. For each creature exiled this way, create a 3/3 white Angel creature token with flying that's tapped and attacking.

Whenever War Priest of Bahet deals combat damage to a player, purge. (Exile two cards that share a type from graveyards. If you do, draw a card.)

Enchant artifact or creature
Enchanted permanent can't attack and its activated abilities can't be activated.

Exile target nonland permanent if its mana value is less than or equal to the greatest number of nonland permanents controlled by a single player.

All creatures get -2/-2 until end of turn. If a creature an opponent controls would die this turn, exile it instead.

Defender (This creature can't attack.)
When Naturebound Druid enters, you may search your library for a basic land card, reveal it, then shuffle and put that card on top.

Advance {2} (Cast this for {2} to advance it as it enters. {2}: Advance this as a sorcery.)
Equipped creature gets +X/+0 and has flying, where X is the number of times it and Jet Pack have advanced this turn.
Equip {1}

[+2]: Look at the top card of your library. If it's a permanent card with mana value less than the number of lands you control, you may put it onto the battlefield.
[–1]: Sacrifice a land. If you do, draw three cards.
[–7]: Destroy up to X target permanents, where X is the number of lands you control.

Lifelink

Target creature you control gets +1/+1 until end of turn. It fights target creature you don't control.