msem-instigator

Pelagic Hydra enters with seven +1/+1 counters on it.
{1}{G}: Put a +1/+1 counter on Pelagic Hydra.
Remove a +1/+1 counter from Pelagic Hydra: It deals 1 damage to target creature blocking or blocked by it.

Create a 1/1 black and red Vampire creature token with menace. If this spell was cast from a graveyard, create two of those tokens instead.
Flashback {3}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Whenever a nontoken creature with mana value 3 or less you control enters, exile it. If you do, create a token that's a copy of it, except it's a Construct creature instead of its other types.

If you would lose the game, instead sacrifice a storied permanent. If you do and your life total is less than 1, it becomes 1.

{T}, Sacrifice Aether Gateway: Create a tapped Plains token, Island token, Swamp token, Mountain token, or Forest token.

Flying
Whenever an embattled creature you control deals combat damage to a player, draw a card. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

First strike
Whenever Creed, Eternal Straggler attacks, exile the top card of your library. You may play that card this turn, and that spell costs {2} less to cast.

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever Crowd Favorite extorts a spell, put a +1/+1 counter on Crowd Favorite.

At the beginning of each upkeep, choose one that hasn't been chosen —
• Exile target tapped nonland permanent.
• Draw two cards, then discard a card.
• Return up to two target permanent cards from your graveyard to your hand.
• Exile Take the City, then return it to the battlefield under your control.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Vigilance, reach, trample
{4}{G}{G}, Exile Qiyan, Serpent of Seven Heads from your graveyard: Create seven 1/1 green Snake creature tokens. Activate only as a sorcery.

Lifelink
Players casting spells and creatures entering don't cause abilities to trigger.

When Attuned Ancient enters, if you control a legendary creature, you may have Attuned Ancient deal damage equal to its power to target creature an opponent controls.

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
When Escort Recruiter becomes renowned, look at the top three cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Whenever a land you control becomes a creature, put a +1/+1 counter on it.
{2}{G}{U}: Target land you control becomes a 3/3 Elemental creature in addition to its other types until end of turn.

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a creature card with mana value equal to the sacrificed creature's mana value minus 1, put it onto the battlefield, then create a token that's a copy of that creature. Then shuffle.

When Horizon Treader enters, you may exile target enchantment you control. Return that card to the battlefield under your control at the beginning of the next end step.

Trial 4 (As you cast this spell, an opponent of your choice may pay 4 life. If they don't, they fail the trial.)
When Treacherous Devil enters, if an opponent passed the trial, that player gains control of Treacherous Devil.

Menace
Evanescent Soulcatcher's power and toughness are each equal to the number of cards in exile.
{2}, Exile a card from your hand: Regenerate Evanescent Soulcatcher.

Target player loses X life and you gain X life, where X is the number of permanents you control with counters on them.

Flying, haste
Thermal Surger can't block.
When Thermal Surger enters, you may sacrifice a land or exile a land card from your graveyard. If you do, put a +1/+1 counter on Thermal Surger.

Until end of turn, target creature you control gains “{T}: This creature deals 1 damage to any target.”
Draw a card.

Venerated Beast can't be blocked by more than one creature.

Choose two —
• Exile target spell.
• Target player may scry 2. If they do, they draw a card.
• Return target artifact card from your graveyard to the battlefield.
• Destroy target nonartifact creature.

At the beginning of combat on your turn, if you control a creature with power greater than Ever-Gnawing Rat's, put a +1/+1 counter on Ever-Gnawing Rat.