msem-instigator

Haste
Augmented — Whenever you cast a spell, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, put a +1/+1 counter on Bolstered Guardian. It loses this ability and gains “Whenever this attacks, it deals 2 damage to each of up to two targets.”

Damage can't be prevented.
At the beginning of your upkeep, Bomb Juggler deals 3 damage to target player chosen at random.

Target creature and all other creatures with the same name as that creature get +2/+0 until end of turn.

When Bone Pit Raptor enters, other creatures you control get +1/-1 until end of turn.
Revive {2}{R} ({2}{R}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

This spell costs {2} less to cast if you control a creature with power 4 or greater.
Bonk deals 4 damage to any target.

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

Assault {R} (Whenever this attacks, if it has no +1/+1 counters on it, you may pay its assault cost to put a +1/+1 counter on it.)
When Borsuppa Outrider assaults, it deals 2 damage to each opponent.

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.

Menace (This creature can't be blocked except by two or more creatures.)
Assault {R} (Whenever this attacks, if it has no +1/+1 counters on it, you may pay its assault cost to put a +1/+1 counter on it.)

Eureka! (At the beginning of each end step, you get a research counter if you cast a spell this turn. Then if you have eight or more research counters, remove them and create a Masterpiece token of your choice.)
When Bottled Lightning enters, it deals 3 damage to any target. Scry 1.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Bounty Crusher has trample as long as it's being blocked by a marked creature.

Harmony — Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”
When Bouquet Singer enters, harmonize. (Trigger up to one harmony of one permanent you control.)

Gain control of target nonland permanent you don't control unless its controller has Bow or Burn deal X damage to them, where X is twice that permanent's mana value. If Bow or Burn was cast from a graveyard, repeat this process for each other nonland permanent they control.
Flashback {6}{R}{R}

First strike
Whenever you cast an instant or sorcery spell, if Branch Breaker dealt combat damage to a player this turn, you may sacrifice Branch Breaker. If you do, copy that spell. You may choose new targets for the copy.

Haste
You may exert Brash Charger as it attacks. When you do, creatures with power 1 or less can't block this turn. (An exerted creature won't untap during your next untap step.)

Sacrifice another creature: Brash Hunter deals 1 damage to any target.
At the beginning of your end step, if three or more creatures died this turn, transform Brash Hunter.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Brazen Chimera can't be blocked except by three or more creatures as long as it has a +1/+1 counter on it.

Haste
Whenever one or more creatures attack, you may discard a card. If you do, draw a card.

Brazen Sacrilege deals 2 damage to any target. Until end of turn, if a red source you control would deal damage to that player or to that permanent's controller, it deals that much damage plus 1 instead.

Haste
At the beginning of your end step, sacrifice Breach Runner unless you return another creature you control to its owner's hand.

Whenever Breakneck Barque becomes blocked by a creature, Breakneck Barque deals 3 damage to that creature.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Vehicle becomes an artifact creature until end of turn.)

Breath of Hao'Tai deals 4 damage to any target.

Flying, trample
Whenever Bretala of Redsky attacks, it gains double strike until end of turn unless defending player sacrifices a creature.

{T}: Add one mana of any color. Spend this mana only to cast an instant or sorcery spell.

Flying, haste
At the beginning of the end step, sacrifice Brightflame Phoenix.
Retrace (You may cast this card from your graveyard by discarding a land card in addition to paying its other costs.)