Contamination

At the beginning of your upkeep, sacrifice Contamination unless you sacrifice a creature.
If a land is tapped for mana, it produces {B} instead of any other type and amount.

Typhoid Rats

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

Erebos, God of the Dead

Indestructible
As long as your devotion to black is less than five, Erebos isn't a creature. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
Your opponents can't gain life.
{1}{B}, Pay 2 life: Draw a card.

Each player loses a third of their life, then discards a third of the cards in their hand, then sacrifices a third of the creatures they control of their choice, then sacrifices a third of the lands they control of their choice. Round up each time.

Void Beckoner

Deathtouch
Cycling {2}{B} ({2}{B}, Discard this card: Draw a card.)
When you cycle Void Beckoner, put a deathtouch counter on target creature you control.

Plaguecrafter

When Plaguecrafter enters, each player sacrifices a creature or planeswalker of their choice. Each player who can't discards a card.

Nettlevine Blight

Enchant creature or land
Enchanted permanent has "At the beginning of your end step, sacrifice this permanent and attach Nettlevine Blight to a creature or land you control."

Spreading Plague

Whenever a creature enters, destroy all other creatures that share a color with it. They can't be regenerated.

Massacre Wurm

When this creature enters, creatures your opponents control get -2/-2 until end of turn.
Whenever a creature an opponent controls dies, that player loses 2 life.

Spread the Sickness

Destroy target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Swamp

Plague Spitter

At the beginning of your upkeep, Plague Spitter deals 1 damage to each creature and each player.
When Plague Spitter dies, it deals 1 damage to each creature and each player.

Swallowing Plague

Swallowing Plague deals X damage to target creature and you gain X life.

Rona, Disciple of Gix

When Rona, Disciple of Gix enters, you may exile target historic card from your graveyard. (Artifacts, legendaries, and Sagas are historic.)
You may cast spells from among cards exiled with Rona.
{4}, {T}: Exile the top card of your library.

Death Cloud

Each player loses X life, discards X cards, sacrifices X creatures of their choice, then sacrifices X lands of their choice.

Pestilence

At the beginning of the end step, if no creatures are on the battlefield, sacrifice Pestilence.
{B}: Pestilence deals 1 damage to each creature and each player.

Pestilence Demon

Flying
{B}: Pestilence Demon deals 1 damage to each creature and each player.

Plague of Vermin

Starting with you, each player may pay any amount of life. Repeat this process until no one pays life. Each player creates a 1/1 black Rat creature token for each 1 life they paid this way.

Plague Wind

Destroy all creatures you don't control. They can't be regenerated.

Grave Titan

Deathtouch
Whenever Grave Titan enters or attacks, create two 2/2 black Zombie creature tokens.