msem-instigator

When Bessie's Brood enters, it fights target creature. (If there are no other creatures, it eats itself.)

[+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.”

Create a 3/3 green Beast creature token, then populate. (Create a token that's a copy of a creature token you control.)

Search your library for a land card, put it onto the battlefield tapped, then shuffle.
Coalesce {5}{G}{G} (You may cast this from your graveyard for {5}{G}{G}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Beyond All Horizons's power and toughness are each equal to the number of lands you
control.

Return all creature and planeswalker cards from your graveyard to the battlefield.

When Beyond the Veil enters, another target nonland permanent phases out. (Treat it and anything attached to it as though they don't exist.)
Nonland permanents you don't control with mana value 3 or less can't phase in.

Create two tapped colorless land tokens named Far-Off Lands with “{T}: Add one mana of any color.” (Then exile this card. You may cast the creature later from exile.)

Bigroot Valley enters tapped.
{T}: Add {R} or {G}.
{1}, {T}: Add one mana of any color.

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

{T}: Add one mana of any color a basic land you control could produce.

When Biohazard enters, 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.

Return up to one target spell to its owner's hand.
Create two 1/1 blue Elemental creature tokens with flying. They can't block this turn.

When Bird Call enters, search your library for a creature card, reveal it, shuffle, then put that card on top.
{2}, {T}: Target creature gets +1/+1 until end of turn.

When Black Cat dies, target opponent discards a card at random.

You lose 1 life and exile the top card of your library. You may repeat this process any number of times. Then put up to two cards exiled this way into your hand.
Coalesce {5}{B}{B} (You may cast this from your graveyard for {5}{B}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Black Hole Musings's power is equal to the number of cards in exile.

Menace
When Blackmoat Bully dies, put a +1/+1 counter and a menace counter on target creature you control.

Equipped creature gets +4/+2 and has first strike, vigilance, and trample.
Equip {3}

When Blackwall's Edge enters, if you control four or more lands, you may have each player conjure a card named Data-Point into their hand. (It's a sorcery that costs {2} with “Draw a card.”)
{T}: Add {C}.
When Blackwall's Edge is destroyed, return it to its owner's hand.

Exile target instant or sorcery card from your graveyard. Copy it. You may cast the copy. (Cast a copy of this spell once while this creature is on the battlefield.)

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.

Blazing Volley deals 1 damage to each creature your opponents control.

({T}: Add {U}, {B}, or {R}.)
Bleak Dominion enters tapped.

When Blessed Spellroot dies, you gain 5 life.

When Blightbringer enters, creatures your opponents control get -1/-1 until end of turn.
Unearth {3}{B} ({3}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

Flying
Blind Eternal can't be blocked by creatures with mana value 2 or less.
{3}, Discard Blind Eternal: Search your library for a noncreature card with a mana ability, reveal it, put it into your hand, then shuffle. Activate only as a sorcery.