msem-instigator

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

Advance {1}{R}{W}{B} (Cast this for {1}{R}{W}{B} to advance it as it enters. {1}{R}{W}{B}: Advance this as a sorcery.)
Whenever Blastburn Angel advances, it gets +1/+1 and gains flying until end of turn. It deals 1 damage to each other creature.

Haste
When Blighted Dullahan dies, you draw a card and you lose 1 life.

{1}{B}, {T}: Target creature gets +2/+2 and gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)
{3}{B}{B}, {T}: Target creature gets -2/-2 and gains winnow until end of turn.

When Blighting Ooze enters, put a -1/-1 counter on each of up to X target creatures.
As long as Blighting Ooze is on the battlefield, it has all activated abilities of each creature with a -1/-1 counter on it.

Sacrifice a creature: Put a +1/+1 counter on Blightroot.
Sacrifice a land: Blightroot gains indestructible until end of turn.

Flash
Blind Blackguard can't block.
When Blind Blackguard enters, target player draws a card, then reveals their hand. You choose a nonland card from that player's hand, then that player puts the chosen card on the bottom of their library.

Vision (Whenever this or another creature you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Blind Soulcaller envisions an instant or sorcery card, you may tap target permanent.

Cycling {2} ({2}, Discard this card: Draw a card.)
{3}{B}{B}, Exile Bloated Visceroid from your graveyard: Create two 2/2 black Zombie creature tokens. Activate only as a sorcery.

When Blood Jade Prophet enters, reveal the top three cards of your library. For each card revealed this way, you may pay 3 life. If you do, put that card into your hand. Otherwise, put it into your graveyard.

Whenever you sacrifice a creature, you may pay {B}{G}. If you do, put a +1/+1 counter on Bloodblade Mercenary and draw a card.

Flying, menace, haste
When Bloodfiend Ravager enters, it deals 2 damage to any target. If a permanent dealt damage this way would die this turn, exile it instead.
Evoke {1}{R} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Flying, haste
{1}{R}{R}: Return Bloodfire Phoenix from your graveyard to the battlefield. Activate only if an opponent lost 3 or more life this turn.

Haste
When Bloodfury Warlord enters or dies, it deals 2 damage to each player.

Whenever you discard a card or an artifact is put into your graveyard from the battlefield, put a +1/+1 counter on Bloodhollow Bruiser.
Cycling {2} ({2}, Discard this card: Draw a card.)

Flash (You may cast this spell any time you could cast an instant.)
When Bloodhunter Orca enters, target opponent sacrifices a creature that was dealt damage this turn.

Bloodline Zealot gets +2/+0 and has menace as long as you've sacrificed a permanent this turn.

Flash
This spell costs {2} less to cast if five or more cards are in your graveyard.

Flying, prowess

When Boneweary Warrior dies, you may put a -1/-1 counter on target creature.

When Border Seeker dies, search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then you gain 1 life for each land you control.

When Borderland Garrison enters, it deals 1 damage to up to one target creature and 1 damage to you.

{G}, {T}, Remove a +1/+1 counter from a creature you control: Create a 2/2 green Ox creature token.

Whenever Borsuppa Roughrider attacks, create a colorless Desert land token named Scoured Path with “{T}: Add {R}.” Sacrifice that token at the beginning of the next end step.