msem-instigator

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.

Haste
{T}: Dragonfire Sniper deals 1 damage to target creature or planeswalker and 1 damage to that permanent's controller.

At the beginning of each end step, if you've cast a noncreature spell this turn, put a +1/+1 counter on Streetwise Spellseeker. Then if its power is 5 or greater, create a 4/4 white Angel Soldier creature token with flying.

Trample
Whenever Fellor Razer deals combat damage to a player, that player sacrifices a land.

Heroic — Whenever you cast a spell that targets Floodspeaker Triton, put a +1/+1 counter on Floodspeaker Triton, then scry 1.

Flash
Whenever Mischievous Capuchin or another Monk you control enters, tap target creature you don't control. If it was already tapped, it doesn't untap during its controller's next untap step.

At the beginning of your upkeep, you may pay {1}{G}. If you do, create a 1/1 green Dryad creature token with “Sacrifice this creature: Add one mana of any color.”

Search your library for up to three creature cards with mana value 2 or less, put them onto the battlefield, then shuffle.

Equipped creature can't have -1/-1 counters put on it.
Equip {1}

Exile target card from a graveyard. If this spell was foretold, create a 2/1 white Soldier creature token.
Draw a card.
Foretell {W} (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.)

Tap two untapped Elves you control: Add {G}{G}.
{6}{G}{G}: Create an 8/8 green Elemental creature token.

Enchant creature
Enchanted creature gets +1/+1, has flying and lifelink, and is a legendary artifact in addition to its other types.

Trample, haste
Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)

Creature spells you cast cost {1} less to cast.
Whenever you attack, target attacking creature you control gets +1/+1 until end of turn. If it's legendary, put a +1/+1 counter on it instead.

Other Foxes you control get +1/+1.
{2}{W}: Target Fox you control gains lifelink until end of turn.

Enchant creature
When Chords of Order enters, put a +1/+1 counter on enchanted creature.
Whenever enchanted creature attacks, tap up to one target creature without a +1/+1 counter on it, then untap up to one target creature with a +1/+1 counter on it.

({T}: Add {W} or {U}.)
Tranquil Stream enters tapped.

Activated abilities of artifacts cost {2} more to activate.

Whenever you gain life for the first time each turn, each opponent loses 2 life.

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.)

Foretell {B}{R} (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.)
Haste
Whenever Sofia deals combat damage to an opponent, exile the top card of that player's library face down and look at it. You may play 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. Then foretell Sofia. It costs {0} to foretell this way.

Whenever Babbling Experiment or another creature you control enters, target player mills two cards.

{T}: Add {W} or {B}.
{W}{B}, {T}: Each opponent loses 1 life and you gain 1 life.

When Naiad of the Glen enters, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)
Naiad of the Glen has trample as long as it has a +1/+1 counter on it.

Tzelin of the Demon Realm can't block.
Whenever a Demon you control enters, you may pay {B}. If you do, return Tzelin from your graveyard to the battlefield with a +1/+1 counter on it.