msem-instigator

First strike
Whenever you scry, Battlewise Paragon gets +1/+1 until end of turn for each card you looked at while scrying this way.

Each creature you control assigns combat damage equal to its toughness rather than its power.
Identity — Other creatures you control get +0/+1 as long as you control at least two other creatures that share a creature type with Battlewise Strategist.

Deathtouch, lifelink
Whenever Batwing Initiate deals combat damage to a player, put a +1/+1 counter on it.
Pay 4 life: Batwing Initiate gains flying until end of turn.

At the beginning of your upkeep, Bauble of Infinites deals 2 damage to each opponent and you gain 2 life.

(Transform this if it's not attached to a creature. Pay {1}{U} as a sorcery to unattach it.)
Enchant creature you control
Bay-Bandit's Snapper's rider gets +1/+2.
Whenever Bay-Bandit's Snapper's rider deals combat damage to a player, you draw two cards.

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

Concord — When Bazaar Equestrian enters, if there are four or more card types among permanents you control, you gain 4 life.

Flash
Haste
{3}, {T}: Exchange control of two target noncreature spells. Their controllers may choose new targets for the spells.

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.

If you would catalyze, catalyze twice instead. (The next spell you cast this turn costs {1} less to cast.)
You may pay an additional {2} as you cast a spell. If you do, reveal the bottom card of your library. You may put it into your graveyard or on top of your library.

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.

Enchant creature
Enchanted creature gets +1/+1.
Sacrifice Bear Necessities: Enchanted creature gains indestructible until end of turn.

Bearer of Fables gets +1/+1 for each enchantment you control.
{2}{G}: Look at the top four cards of your library. You may reveal an enchantment card or a card with fabled from among them and put it into your hand. Put the rest on the bottom of your library in any order.

When Bearer of Silk Chains enters, gain control of target nonland permanent until Bearer of Silk Chains leaves the battlefield. If that permanent is a Horror, gain control of it instead.

When Bearer of Tormented Truths enters, look at target player's hand. You may exile a nonland card from among them. If you do, that player draws a card.
You may play cards exiled with Bearer of Tormented Truths, and you may spend mana as though it was mana of any color to cast them.

Inspired — Whenever Bearer of Vile Incense becomes untapped, create a 0/1 black Cultist creature token with “{1}{B}{B}, Sacrifice three Cultists: Create a 5/5 black Demon creature token.”

Equipped creature has menace and trample.
Equip {2}

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.)

Whenever you detain a permanent, you gain life equal to that permanent's mana value.

{2}, {T}: Tap target creature.

Reveal the top three cards of your library. Put all creature cards revealed this way into your hand and the rest into your graveyard.

Whenever you cast an instant or sorcery spell, each opponent loses 1 life and Beast of Pestilence gets +1/+1 until end of turn.

Desecrate (When this creature enters, you may sacrifice an artifact or land.)
When Beastback Raider desecrates a permanent, discard your hand, then draw three cards.

{T}: Add {G}.
{T}: Add {G}{G}. Activate only if you control an Elemental.