msem-instigator

Flying
When Ascended Explorer enters, return target creature card with mana value 2 or less from your graveyard to the battlefield.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Ash Breather deals combat damage to a player, you may discard a card. If you do, draw a card.

Ash Freebooter has first strike as long as it's attacking.
When Ash Freebooter enters, you may discard a card. If you do, draw a card.

Put any number of target creature cards from your graveyard on top of your library. You draw two cards and you lose 2 life.

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
This creature can't be blocked by creatures with power 1 or less.

Ashthread Alley enters tapped.
{T}: Add {B} or {R}.
{B}{R}, {T}, Sacrifice Ashthread Alley: Conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

Whenever Aspect of An'yama attacks, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)
Spells you cast from your graveyard, activated abilities of cards in your graveyard, and reprise costs of spells you cast cost {1} less.

Choose two —
• Tap target creature.
• Untap target creature.
• Draw a card.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever a creature you control deals combat damage to a player, you may have Aspect of Rage deal 1 damage to any target.

When Asphodel Gravedealer dies, choose one —
• Put a +1/+1 counter on target creature you control.
• Create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Whenever a storied permanent you control enters, tap target creature an opponent controls. (Enchantments and legendary permanents are storied.)

Aspiring Dragon has flying and haste as long as you control another Dragon.
{2}{R}{R}: Aspiring Dragon gets +3/+0 until end of turn.

Rhapsody {3}{W}{W} (Pay {3}{W}{W} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Lifelink

Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 until end of turn.

Flash
When Assassin of Fahrib enters, choose one —
• Destroy target creature that was dealt damage this turn.
• Scry 2.

Target creature gets -3/-0 until end of turn. That creature's controller mills six cards.

Destroy target tapped creature.

Destroy target creature. Create a tapped Treasure token.

Creatures you control get +2/+0 until end of turn. Untap each Army you control.

Create three 1/1 colorless Construct Actor creature tokens.

Target creature gets -5/-0 until end of turn. Adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)

Menace
Once during each of your turns, when you sacrifice a permanent, you may put a +1/+1 counter on Assimilated Runner.

When Assurance of Finality enters, you may discard a card. If you do, draw two cards.
{1}, Sacrifice Assurance of Finality: Creatures you control gain haste until end of turn.

Target player sacrifices a creature or planeswalker.
Flashback {4}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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.)