msem-instigator

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
At the beginning of each end step, if you lost life this turn, you may pay {1}. If you do, create a 2/2 black Zombie creature token.

As long as you've gained life this turn, Bloodied Outcast gets +1/+0 and has lifelink.
As long as an opponent has lost life this turn, Bloodied Outcast gets +0/+1 and has deathtouch.

{1}, {T}, Sacrifice another creature: Put a +1/+1 counter on Bloodied Wulfhound.

Sacrifice a creature: Put a +1/+1 counter on Bloodlash Caravan. Then if it's the only creature you control, it gains indestructible until end of turn.

Bloodleaf Butcher gets +1/+0 and has deathtouch as long as five or more cards are in your graveyard.

Frenzy 1 (Whenever this creature attacks and isn't blocked, it gets +1/+0 until end of turn.)

Flying
{1}, Sacrifice another creature: Regenerate target Vampire.

Haste
Bloodvenge Berserker doesn't untap during its controller's untap step.
Once each turn, when an opponent is dealt damage by another source you control, you may untap Bloodvenge Berserker.

At the beginning of each player's end step, if they aren't horrific, Bloody Valentine deals 2 damage to that player. (You're horrific as long as you've sacrificed a permanent or discarded a card this turn.)

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 another creature you control enters, you may have it gain haste. If you do, return it to its owner's hand at the beginning of the next end step.

Menace
When Bogborn Exorcist enters, you may discard a card. When you do, exile target instant or sorcery card with mana value 3 or less from an opponent's graveyard. Copy that card. You may cast the copy without paying its mana cost.

Flying, first strike

Whenever Bold Vanquisher attacks, upgrade it. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• Trample

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

Assault {1}{B} (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 Bone Mesa Marauder assaults, it gains flying until end of turn.

As long as an opponent has two or fewer cards in their hand, Bonespitting Monstrosity gets +2/+2 and has menace and “Whenever Bonespitting Monstrosity attacks and isn't blocked, create a 1/1 black Skeleton creature token.”

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

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

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.

{B}, {T}: Post a bounty on target permanent. (Put a bounty counter on that permanent. It has “When this permanent is put into a graveyard from the battlefield, each opponent draws a card” as long as it has a bounty counter on it.)
{B}, {T}, Pay 2 life: Destroy target creature with a bounty counter on it.

Whenever a creature with a counter on it dies, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Other Hounds you control get +1/+1.

When Braenid Nomad enters, draw two cards, then discard a card.