msem-instigator

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.

When Bleeding-Edge Garroter dies, if it was in a pack, you draw a card and you lose 1 life. (Two or more creatures you control with equal power are in a pack.)

Blighted Unicorn can't block.
Ride {3}{B} ({3}{B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

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.

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
At the beginning of your end step, each cursed opponent loses 2 life unless they discard a card.

Lifelink
Revive {3}{B} ({3}{B}, Exile this card from your graveyard: Create a token that's a copy of this card, except it has no mana cost. Activate this ability only any time you could cast a sorcery.)

When Blisterbug dies, put two +1/+1 counters on target creature you control.

Advance {1}{R} (Cast this for {1}{R} to advance it as it enters. {1}{R}: Advance this as a sorcery.)
Whenever Blitz Breaker advances, its power becomes equal to the amount of noncombat damage that's been dealt to your opponents this turn. (This effect lasts indefinitely.)

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.

Engorge (As this enters, mill three cards, then exile a card from among the milled cards.)
When Blood Servant enters, if it engorged a creature card, you draw a card and you lose 2 life.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Target creature you control gets +1/+0 until end of turn.
[Lore III] Target creature you control gets +2/+0 until end of turn.

Improve {1}{R} ({1}{R}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
As long as Bloodbelly Glutton is embattled, it has first strike, menace, and haste. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

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.

{B}, Discard a card: Bloodbraid Ritualist gains indestructible until end of turn. Tap it.
At the beginning of your upkeep, you may have Bloodbraid Ritualist consume. If you do, draw a card. (To consume, sacrifice another creature or exile a creature card from your graveyard.)

When Bloodbriar Acolyte dies, draw a card. Each opponent loses 1 life.

Deathtouch
{T}, Sacrifice another creature: Add two mana of any one color.

Sacrifice another creature: Put a +1/+1 counter on target creature you control. Activate only as a sorcery.

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.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When Bloodied Twinblade dies, scry 1. (To scry 1, look at the top card of your library. You may put that card on the bottom of your library.)

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

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

{G}, {T}: Put a +1/+1 counter on Bloodleaf Tracker for each creature that entered this turn.