Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Marshmist Titan

This spell costs {X} less to cast, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Doom Blade

Cast Down

Terror

Destroy target nonartifact, nonblack creature. It can't be regenerated.

Swamp

Sign in Blood

Target player draws two cards and loses 2 life.

Cadaver Imp

Flying
When Cadaver Imp enters, you may return target creature card from your graveyard to your hand.

Deathgaze Cockatrice

Flying
Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Ruthless Ripper

Deathtouch
Morph—Reveal a black card in your hand. (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Ruthless Ripper is turned face up, target player loses 2 life.

Fleshbag Marauder

When Fleshbag Marauder enters, each player sacrifices a creature.

Black Cat

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

Doomed Dissenter

When Doomed Dissenter dies, create a 2/2 black Zombie creature token.