msem-instigator

Prowess
Other Monks you control get +1/+1.
Whenever you cast a spell during another player's turn, untap each Monk you control.

Rhapsody {4}{R}{R} (Pay {4}{R}{R} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Trample
Whenever Attuned Slayer deals combat damage to a player, exile that many cards from the top of your library. You may play those cards this turn.

Haste
Augmented — At the beginning of combat on your turn, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, gain control of target nonland permanent until end of turn. Untap it. It gains haste until end of turn.

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.)

{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.

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.

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.

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.

Menace
Whenever Auros, Flame-Cursed attacks, it deals 3 damage to each opponent.

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.