msem-instigator

Tribute 3 (As this creature enters, an opponent of your choice may put three +1/+1 counters on it.)
When Atuum Serpent enters, if tribute was paid, it gains defender. (This effect lasts indefinitely.)

Target player reveals their hand. You choose a nonland card from it. That player discards that card. Each player loses 1 life.

You may put a +1/+1 counter on target creature you control. It deals damage equal to its power to another target creature or planeswalker.

{2}{W}: Audacious Knight gains first strike and vigilance until end of turn. (It deals combat damage before creatures without first strike. Attacking does not cause it to tap.)

{1}, Sacrifice a creature or enchantment: Exile the top card of your library. You may play that card this turn.

You may put a creature card from your hand onto the battlefield. That creature gains haste until end of turn. Sacrifice that creature at the beginning of the next end step unless you pay its mana cost reduced by up to {3}{R}{R}.

Counter target spell. If you are glorious, draw a card. (You are glorious as long as you have a glory counter.)

When Augmented Alchemist enters or dies, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

Flash
When Augmented Spawn enters, create a 1/1 blue Merfolk creature token for each Island you control.
{U}, Sacrifice a Merfolk: Augmented Spawn gains hexproof until end of turn.

Flying
When Augur of Bleak Horizons enters, you gain 3 life and you mill three cards.

Flying
Other creatures you control with flying get +1/+1.

Augury Hydra enters with X +1/+1 counters on it.
When Augury Hydra enters, scry Y, where Y is its power, then draw Y cards.

Flying
Whenever August Sunbird attacks, create a token that's a copy of another target creature you control, except it's 1/1, and it's tapped and attacking. Sacrifice the token at the beginning of the next end step.

Menace, haste
At the beginning of combat on your turn, gain control of up to two target noncreature, nonland permanents your opponents control until end of turn. Untap those permanents. You may attach any number of Equipment among them to creatures you control until end of turn. (They unattach at end of turn.)

Whenever Aukashi, Electric Legacy enters or equipped creature dies, attach Aukashi to a creature you control.
Whenever equipped creature deals damage to a permanent or player, Aukashi deals 2 damage to that permanent or player.
Equipped creature has double strike as long as a creature you controlled died this turn.
Equip {2}

Whenever equipped creature deals combat damage to a player, exile an instant or sorcery card from your graveyard. Then copy any number of cards exiled with Aukashi, the Rising Storm with mana value X or less and cast the copies without paying their mana costs, where X is the number of cards exiled with Aukashi.
Equip {2}

This spell can't be countered.
Flying
When Aunor, Dragonsire or another Dragon you control enters, untap target land. That land becomes a 5/5 Dragon creature with flying and haste in addition to its other types.

Enchant creature
When Aura of Leadership enters, create four 1/1 white Human Soldier creature tokens.
Enchanted creature gets +2/+2.

When Auramancer enters, you may return target enchantment card from your graveyard to your hand.

Target player sacrifices an enchantment.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, return up to one enchantment card from your graveyard to your hand.

When Aureate Golem enters, create a Treasure token. Each other player creates a tapped Treasure token. (They're artifacts with “{T}, Sacrifice this artifact: Add one mana of any color.”)

{1}, {T}, Sacrifice Aureate Panorama: Search your library for a land card that could produce each color of mana, put it onto the battlefield, then shuffle.

This spell can't be countered.
Hexproof

Flying
At the beginning of your end step, if you cast no spells this turn, scry 2.

Counter target creature spell. Scry 2.
Foresee — As you draw Aurora's Whisper, you may reveal it and pay {U}. When you do, return target creature with mana value 3 or less to its owner's hand.