msem-instigator

Flying, trample
Prismatic — Whenever you cast a multicolored spell, put a +1/+1 counter on Azure Caterwauler.

When Backstage Broken enters, create a 1/1 colorless Construct Actor creature token.
Whenever a token you control leaves the battlefield, you gain 1 life.

Flying
{B/G}, Discard a creature card: Badru, the Skyshadow becomes a copy of the discarded card until end of turn, except he has flying and is 5/5.

Whenever Baljurn, the Runelord or another nontoken artifact or enchantment you control enters, create a 0/0 blue Construct artifact creature token. Put a +1/+1 counter on each artifact and/or enchantment creature you control other than Baljurn.

Whenever Barker Duelist becomes blocked, defending player loses 1 life.
Unveil {3}{B}{R} ({3}{B}{R}: Transform this. Unveil only as a sorcery.)

When Battlefield Tiger enters, create two 1/1 white Soldier creature tokens.

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

Whenever Beatrice's Dodger attacks, create a 1/1 black and red Human Rogue creature token that's tapped and attacking.
{3}{B}{R}: Return Beatrice's Dodger from your graveyard to the battlefield
tapped and transformed.

Flash
Lifelink
When this creature enters, counter target spell unless its controller pays {1} or 3 life.

Choose target creature with the greatest power or tied for the greatest power, then destroy all other creatures.

Prevent all combat damage that would be dealt to and dealt by Bereaved Aristocrat.
Unveil {2}{W}{U} ({2}{W}{U}: Transform this. Unveil only as a sorcery.)

At the beginning of your upkeep, mill a card.
Whenever a creature card is put into your graveyard from anywhere, if that card has flying, you may put a flying counter on Berylscale Alaj. Repeat this process for first strike, double strike, deathtouch, hexproof, lifelink, menace, reach, trample, and vigilance.

Return to your hand all permanent cards in your graveyard that were put there from the battlefield this turn.

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.

When Blinding Fiddler enters, until your next turn, creatures can't attack you or a planeswalker you control unless their controller pays {2} for each of those creatures.
Unveil {3}{W}{U} ({3}{W}{U}: Transform this. Unveil only as a sorcery.)

When Blossom-Sower Witch enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice a permanent, you gain 1 life.

Whenever this creature or another creature you control dies, this creature deals 1 damage to each opponent.

If you would draw a card, you may instead choose creature or land and exile cards from the top of your library until you exile a card of the chosen kind. Put that card into your hand and put all other cards exiled this way on the bottom of your library in a random order.

Prowess
Unveil {2}{U}{R} ({2}{U}{R}: Transform this. Unveil only as a sorcery.)

Flash
Whenever you cast your second spell each turn, put a +1/+1 counter on Brooding Replacement.

Double strike
Whenever you cast a noncreature spell, you may choose one that hasn't been chosen —
• Tap or untap target permanent.
• Draw two cards, then discard a card.
• Creatures you control get +1/+1 until end of turn.

Whenever another creature enters, Brutish Champion fights that creature.

Bwema, the Ruthless enters with your choice of two different counters on it from among menace, first strike, vigilance, and lifelink.

When this creature enters, if you cast it, return target permanent card with mana value 3 or less from your graveyard to the battlefield tapped.
Whenever this creature attacks, you may sacrifice a nonland permanent. If you do, it gets +1/+1 and gains indestructible until end of turn.