msem-instigator

When Barbarian Intimidator enters the battlefield, target creature can't block this turn.
When Barbarian Intimidator enters the battlefield, prevent all combat damage that would be dealt to target creature this turn.

Whenever Barker Duelist becomes blocked, defending player loses 1 life.
Unveil {3}{B}{R} ({3}{B}{R}: Transform this. Unveil only as a sorcery.)

Vigilance
Whenever Bartimus attacks, another target attacking creature gets +1/+1 until end of turn. If that creature is a Soldier, put a +1/+1 counter on it instead.

When Basalt Ritualist enters the battlefield, you may sacrifice a land or exile a land card from your graveyard. When you do, exile target creature, instant, or sorcery card from your graveyard. Until the end of your next turn, you may play that card. If that spell would be put into a graveyard, exile it instead.

When Batrest's Forgemaster enters the battlefield, you may search your library for an Equipment card, reveal it, put it into your hand, then shuffle.
Whenever Batrest's Forgemaster attacks, Equipment spells you cast this turn cost {2} less to cast.

Batrest, Fellor Leader gets +1/+1 for each Equipment attached to it.
When Batrest enters the battlefield, create Astrina, Forged for Glory, a legendary colorless Equipment artifact token with “Equipped creature gets +4/+4 and has first strike and lifelink” and equip {4}. Attach it to Batrest.

Return any number of target creature cards with total mana value X or less from your graveyard to the battlefield, where X is the number of cards in your graveyard. Exile Battle at the Boneyard.

Battalion — Whenever Battleborn Brute and at least two other creatures attack, Battleborn Brute gets +2/+2 until end of turn. Untap it.

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.

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

When Bearer of Tormented Truths enters the battlefield, 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.

Whenever Beatrice's Dodger attacks, create a 1/1 black and red Human Rogue creature token that's tapped and attacking.
{3}{B}{R}: Return Beatrice's Dodger from your graveyard to the battlefield
tapped and transformed.

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

Creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, Bellowing Thoctar gets +2/+2 until end of turn.

Choose target creature with the greatest power or tied for the greatest power, then destroy all other creatures.

Aetherize each permanent you control. Exile Beneath the Horizon. (To aetherize a permanent, create a token that's a copy of it, then exile that token.)

Whenever Beragnian Brawlmaster or another Warrior enters the battlefield under your control, that Warrior fights target creature an opponent controls.
{R}{W}: Target Warrior creature gets +1/+1 until end of turn.

Prevent all combat damage that would be dealt to and dealt by Bereaved Aristocrat.
Unveil {2}{W}{U} ({2}{W}{U}: Transform this. Unveil only as a sorcery.)

At the beginning of your upkeep, mill a card.
Whenever a creature card is put into your graveyard from anywhere, if that card has flying, you may put a flying counter on Berylscale Alaj. Repeat this process for first strike, double strike, deathtouch, hexproof, lifelink, menace, reach, trample, and vigilance.

[+2]: Create a 3/3 red Wurm creature token.
[–2]: Up to three target creatures each get +2/+2 until end of turn. Bessie deals 2 damage to each of up to three target creatures.
[–9]: You get an emblem with “Creatures you control have base power and toughness 7/7 and have indestructible.”

Bestial Mob's power and toughness are each equal to the number of creatures you control.
Whenever Bestial Mob deals combat damage to a player, destroy target creature with toughness less than Bestial Mob's power.

You may have Better Half enter the battlefield as a copy of any creature on the battlefield, except it's a Reflection in addition to its other creature types and it has distorted. (It can be blocked by tapped creatures but not untapped creatures.)

Trample, haste, indestructible
Whenever a permanent an opponent controls is put into a graveyard from the battlefield, put a +1/+1 counter on target Ooze.

When Bind the Mind enters the battlefield, each poisoned opponent reveals their hand. Then choose a nonland card name.
Spells with the chosen name can't be cast.

When Biohazard enters the battlefield, destroy all other nonland permanents with mana value X or less.
At the beginning of each end step, each opponent loses life equal to the number of cards they've drawn this turn plus the number of spells they've cast this turn.