msem-instigator

When Astrid, Disgruntled Princess enters, destroy target creature with mana value less than or equal to the number of Warriors you control.

When Astute Sceneweaver enters, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Flying
When Atieh's Elite enters, judge another target creature you control. (Honor it by putting a +1/+1 counter on it or condemn it by sacrificing it to draw a card.)
Whenever you honor a creature, until end of turn, that creature has base power and toughness 4/4, gains flying, and becomes an Angel in addition to its other types.

Flying, vigilance, lifelink
Whenever Atieh's Favored attacks, put a +1/+1 counter on each other Angel and/or Nephilim creature you control.

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.

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

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.

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

Flying
Spirited (When this creature enters, you may activate one of its activated abilities without paying its costs.)
{3}{U/B}{U/B}: Look at the top card of target opponent's library, then exile it face down. You may play that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell.

Flying
When Aven Merchant enters, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Flying
When Aven Strategist enters, return up to one target creature to its owner's hand.

This spell costs {2} less to cast if a creature died under your control this turn.
Flying

This spell can't be countered.
Survivor spells you cast can't be countered.
Whenever a nontoken Survivor you control enters, create a tapped 1/1 Survivor creature token that's all colors.

Flash
When Axom enters, remove up to three counters from target permanent.
{2}{U}: Return Axom to its owner's hand.

When Azure Archaeologist enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
{2}, {T}, Sacrifice a Clue: Draw two cards, then discard a card.

When Azutahn Hydromancer enters, you may return target creature with power X or less to its owner's hand, where X is the number of differently named lands you control.

Desecrate (When this creature enters, you may sacrifice an artifact or land.)
When Back-Alley Vandal desecrates a permanent, put a +1/+1 counter on Back-Alley Vandal.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever Backalley Silencer deals combat damage to a player, destroy target marked creature.

Haste
When Backdrop Artisan dies, audition for red. (Create a 1/1 Construct Actor creature token, a Warrior Role giving 3/2 and trample, or a Wizard Role giving 2/2 and prowess. Roles replace older ones.)

Basic Forests you control have “{G}, {T}: Untap target attacking creature and remove it from combat.”

Whenever you create one or more tokens, put a +1/+1 counter on target creature you control.
{2}{G}{W}: Create a 0/1 green Plant creature token.

Prowess
Whenever Balefire Conjurer attacks, you may pay {1}{R}. If you do, exile the top card of your library. You may play that card until the end of your next turn.