msem-instigator

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.

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.

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)
During each of your turns, you may cast an instant or sorcery spell from your graveyard. If that spell would be put into your graveyard, exile it instead.
Whenever Aurora, Soulweaver attacks, untap any number of target creatures.

This spell can't be countered.
When Auros enters, it deals damage to any target equal to your devotion to red. (Each {R} in the mana costs of permanents you control counts toward your devotion to red.)
{R}, Sacrifice Auros, Discard your hand: Draw three cards.

Trample
Auspicious Qilin must be blocked if able.

Once each turn, when you cast a noncreature spell, create a 1/1 colorless Human creature token. Put a prowess counter on it.

Whenever you play a land, return a card at random from your graveyard to your hand.
Whenever you cast a green spell, reveal the top card of your library. If it's a land card, put it into your hand. Otherwise, mill it.

Exile target tapped creature. Its controller gains 3 life.

When Automated Blademaster enters, create a colorless Equipment artifact token named Sword with “Equipped creature gets +1/+1” and equip {1} and attach it to Automated Blademaster.

Harmony — Scry 2.
{T}: Harmonize. Activate only as a sorcery. (Trigger up to one harmony of a permanent you control.)

Reach
When Automated Overwatch enters, create a Function token with “If this spell would create one or more tokens, it creates twice that many of those tokens instead.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

({T}: Add {R} or {G}.)
Autumn Canopy enters tapped.
{1}, {T}: Add {R}{R} or {G}{G}.

Flying, double strike
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

{T}: Add {C}.
{2}, {T}: Add three mana of any one color.

Creatures you control get +1/+0 and gain haste until end of turn.