msem-instigator

Flash
When Blade of Mautakesh enters, creatures you control gain poisonous 1 until end of turn. (Whenever those creatures deal combat damage to a player, that player gets a poison counter. Multiple instances of poisonous trigger separately.)

Double strike
Attain {3}{R} ({3}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

{1}{R/W}: Untap Blade of the Long Night.

Equipped creature gets +1/+1 and has haste.
Whenever a creature you control enters, if it was cast from exile, you may attach Blade of the Valiant to it.
Equip {2}

Invigorate X, where X is the number of creatures you control. (Choose a creature with the least power among creatures you control and put X +1/+1 counters on it.)

Blazing Beam deals 4 damage to any target.

Trample, haste
When Blazing Fox enters, you may tap an untapped creature you control. If you do, Blazing Fox gets +X/+0 until end of turn, where X is that creature's power.

Blazing Offerings deals 4 damage to target creature or planeswalker.

({T}: Add {U}, {B}, or {R}.)
Bleak Dominion enters tapped.

When Bleak Gorge Convoy enters, you may search your library for a Desert card, put it onto the battlefield tapped, then shuffle.

Flying
Menagerie — When Bleakrealm Mini-Menace enters, if there are five or more creature types among creatures you control, it deals 2 damage to target opponent and 2 damage to up to one target creature or planeswalker that player controls.

Discard your hand, then draw two cards.
Agonize (You may cast this card from your graveyard by putting a -1/-1 counter on a creature you control in addition to paying its other costs. Then exile this card.)

Blessed Barrage deals 5 damage divided as you choose among any number of attacking or blocking creatures.

({T}: Add {W} or {B}.)
As Blessed Mausoleum enters, you may pay {1}. If you don't, Blessed Mausoleum enters tapped.

When Blessing from Wings on High enters, you may search your library for an Angel or Nephilim card, reveal it, put it into your hand, then shuffle.
Creatures you control get +1/+0.

Gestalt (When this or another creature you control enters, 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 permanent gets +2/+2 for each card and token merged with it.

Distribute three +1/+1 counters among one, two, or three target creatures you control.

Put a +1/+1 counter on target creature you control.
Monument {1}{G} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

Whenever one or more creatures an opponent controls attack you or a planeswalker you control, that player gets a poison counter.

When Blessing of Roya enters or whenever you cast a spell from a graveyard, you gain 5 life and you mill five cards. Then you may put a card from your graveyard on the bottom of your library.

Whenever you cast an instant or sorcery spell from exile, copy it. You may choose new targets for the copy.

When Blightbringer enters, creatures your opponents control get -1/-1 until end of turn.
Unearth {3}{B} ({3}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

Equipped creature gets +2/-1.
Equip {1}

Whenever one or more creatures attack you, you may put a -1/-1 counter on target creature.

Blighted Unicorn can't block.
Ride {3}{B} ({3}{B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)