msem-instigator

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.

Other creatures you control have haste.
Whenever Breach Titan enters or attacks, abound. (To abound, you may cast a spell that costs less than this from your hand without paying its mana cost.)
At the beginning of your end step, return another target creature you control to its owner's hand.

Flying

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.

Deathtouch
When Brig of the Damned enters, return target creature card from your graveyard to your hand. If that card's mana value is 2, you may return it to the battlefield instead.
Crew 2 (Tap any number of creatures you control with total power 2 or greater: This Vehicle becomes an artifact creature until end of turn.)

Augmented — Whenever Bril, the Oltenen Emissary enters or attacks, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, destroy target permanent.

{T}: Brimstone Grenadiers deals 1 damage to target player.
Whenever you cast an instant or sorcery spell, untap Brimstone Grenadiers.

Defender
When Brine Duelist enters, create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)
{W}{U}{B}{R}{G}: Put a +1/+1 counter on Brine Duelist. It loses defender.

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.

{6}{U}: Brume Trench-Thrasher can't be blocked this turn. This ability costs {1} less to activate for each instant and sorcery card you own in exile and in your graveyard.

Ward {2}
Whenever Brunig enters or attacks, you may shuffle a card you own from outside the game into your library. If you do, you gain 2 life.
Brunig gets +2/+2 and has trample as long as your library contains at least forty cards more than the minimum deck size.

Whenever a creature you control becomes the target of a spell or ability, counter it unless its controller pays {1}. Whenever they do, put a +1/+1 counter on Brushcover Elf. (This includes your spells and abilities.)

Whenever another creature enters, Brutish Champion fights that creature.

When Bubbledome Chorister enters, create a green Aura enchantment token named Sanctum's Gift attached to target creature. The token has enchant creature and “Enchanted creature has ‘{T}: Add {G} for each enchanted creature you control.'”

Whenever you cast an enchantment, instant, or sorcery spell, create a 1/1 blue Jellyfish enchantment creature token with slipstream. (It can't be blocked as long as only creatures with slipstream are attacking.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Concord — As long as there are four or more card types among permanents you control, Bubbledome Waveblade gets +1/+1.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
When Budding Companion has three or more +1/+1 counters on it, remove them all and transform it.

Whenever you foretell a card or cast a foretold spell, Bugrund's Schemer deals 2 damage to each opponent.

Double strike, vigilance
At the beginning of combat on your turn, create X 1/1 red Dwarf creature tokens with haste, where X is the number of embattled nontoken creatures you control. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

Flying
Whenever a permanent you control becomes the target of a spell or ability you don't control, choose one —
• Create a 3/3 red Manticore creature token.
• Create two Treasure tokens.
• Draw a card.

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

Whenever Byway Bruiser enters or leaves the battlefield, you may have it deal 3 damage to any target.

Trample
Whenever Cacophonous Demon deals combat damage to a player or planeswalker, you may exile target artifact or enchantment.
Whenever a creature deals damage to you, tap that creature. It becomes an enchantment in addition to its other types.

When Cadalon Experimenter enters, if you control an artifact, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Menace
Caer Crann Insurgent gets +2/+0 as long as you've foretold a card or cast a foretold spell this turn.