msem-instigator

When Abyssal Nightcaster enters, each player exiles a card from their hand.
When Abyssal Nightcaster dies, you may play cards you don't own from exile this turn.

{B}, {T}, Discard a card: Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Double strike

Non-Human creatures you control get +1/+0.

At the beginning of your upkeep, you may reveal a creature card from your hand. If you do, create a token that's a copy of it, except it's 1/1 and is an artifact in addition to its other types.

When Acolyte of Night dies, each opponent loses 1 life.

At the beginning of your upkeep, if you control four or more Swamps, you may exile target creature card from your graveyard. If you do, create a tapped token that's a copy of it except it's a black Mummy.

{T}: Add one mana of any type that a land an opponent controls could produce.

Converge — Admin of Asthenia enters with a +1/+1 counter on it for each color of mana spent to cast it.
Admin of Asthenia can't attack unless its power is 4 or greater.

Whenever you cast an Adventure spell, put a +1/+1 counter on Adventurer Extraordinaire.

First strike
Whenever a player loses life, creatures you control get +1/+0 until end of turn.

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Heroic — Whenever you cast a spell that targets Aegis Hero, put a +1/+1 counter on Aegis Hero.

Flash
When you cast Aether Ascendant, you may have it become a copy of target instant or sorcery spell. If you do, choose new targets for it. (It won't enter.)

Spells you cast from anywhere other than your hand cost {1} less to cast.
Whenever an opponent casts a spell with the same name as a card they own in exile or in their graveyard, that player loses 1 life and you gain 1 life.

Whenever you make first contact, you may draw a card. If you do, put a card from your hand on the bottom of your library. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

Flash
When Aethermancer's Familiar enters, at the beginning of the next end step, you may aetherize target creature you control. (To aetherize, create a token that's a copy of it, then exile that token.)

When Affluent Knight enters, recruit, then recruit again. (To recruit, create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)

When Ageless Weaver enters, create a green Aura enchantment token named Years of Experience attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2.”
Whenever an enchanted creature you control dies, create a 3/3 green Elemental creature token.

Flash
When Agent of Deception enters, counter target creature or planeswalker spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Deception {1}{B}
When Aguri, Shadow of Doubt enters, target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Ainok Alpha can't be blocked by more than one creature.
Other Hounds you control get +1/+1 and can't be blocked by more than one creature.

Rapport — Whenever Ainok Lout and at least one other creature you control become tapped, Ainok Lout gets +2/+0 until end of turn.

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
When Aith Aera Sentinel enters, create a 1/1 green Elf creature token.

Vigilance
{1}{G}: Ajani's Advocate gets +2/+2 until end of turn. Activate only once each turn.

Haste
Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{1}{R}: Akaima Rager gets +1/+0 until end of turn.