msem-instigator

Put a +1/+1 counter on each creature you control. Creature tokens you control gain vigilance until end of turn.

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

When Bauble Collector enters, you may return another permanent you control to its owner's hand.

When Bayou Courier enters, you may pay 2 life. If you do, create a 3/2 green Crocodile creature token with trample.

Whenever Bazaar Informant deals combat damage to a player, reveal the top card of that player's library. If it's a nonland card, put a +1/+1 counter on Bazaar Informant, then that player puts that card into their graveyard.

Beachhead Partisan has first strike as long as it's attacking.
When Beachhead Partisan enters, it deals X damage to any target, where X is the number of tapped creatures you control.

When Bearer of the Lantern enters, you gain 3 life.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Whenever an artifact or enchantment you control enters, you may detain target nonland permanent. (Until your next turn, that permanent can't attack or block and its activated abilities can't be activated.)

Look at the top two cards of your library. Put one of them into your hand, then submerge the other. (To submerge a card, exile it, then put it on the battlefield face down under its owner's control as a 2/2 creature.)

Return up to one target creature card and up to one target noncreature permanent card with total mana value 4 or less from your graveyard to the battlefield.
Exile Beckon the Damned.

Draw a card, then create a 1/1 blue Elemental creature token. If you drew three or more cards this turn, create three of those tokens instead.

Whenever you cast an enchantment spell, you draw a card and you lose 1 life.
Whenever one or more counters are put on an enchantment you control, you gain 1 life and each opponent loses 1 life.

Bedfellow can't block or be blocked.
Exile two cards from your graveyard: Bedfellow gets +1/+1 until end of turn.

{T}: Add one mana of any color.
{2}, {T}: Put a lore counter on a Saga you control.

Insects you control have hexproof.
At the beginning of your end step, if you control a nontoken Insect, create a 1/1 green Insect creature token.

At the beginning of combat on your turn, target creature you control has base power and toughness 5/5 until end of turn.

When Belief in the World enters, you may tap two untapped creatures you control. If you do or you control two or more Spirits, search your library for a Spirit card, reveal it, put it into your hand, then shuffle.
Creatures you control get +1/+1.

Trample
Whenever Belligerent's Augur or another Warrior you control deals combat damage to a player, you may pay {1}{U}. If you do, draw a card.

Whenever a creature you control dies, you may search your library for a creature card with lesser mana value, put it onto the battlefield tapped, then shuffle. Do this only once during each of your turns.

Other Knights and Soldiers you control get +1/+0.
Cowards can't block Knights and Soldiers you control.
When Belmord Bloodcurdler enters, target creature an opponent controls becomes a Coward in addition to its other types. (This effect last indefinitely.)

Destroy target artifact or enchantment.
Draw a card.

When Benign Whisper enters, return another target creature to its owner's hand.

When Benthic Alchemist enters, draw a card, then discard a card, then mill a card.
Whenever you cast an instant or sorcery spell, create a 1/1 colorless Elemental creature token. It gains haste until end of turn.

Whenever equipped creature attacks, it gets +X/+0 until end of turn, where X is its power.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)