Ophiomancer

At the beginning of each upkeep, if you control no Snakes, create a 1/1 black Snake creature token with deathtouch.

Eaten Alive

As an additional cost to cast this spell, sacrifice a creature or pay {3}{B}.
Exile target creature or planeswalker.

Ossuary Rats

When Ossuary Rats enters, it deals X damage to target creature or planeswalker an opponent controls, where X is the number of creature cards in your graveyard.

Durable Coilbug

{4}{B}: Return Durable Coilbug from your graveyard to your hand.

Swarm of Bloodflies

Flying
Swarm of Bloodflies enters with two +1/+1 counters on it.
Whenever another creature dies, put a +1/+1 counter on Swarm of Bloodflies.

Blight Keeper

Flying
{7}{B}, {T}, Sacrifice Blight Keeper: Target opponent loses 4 life and you gain 4 life.

Grotesque Mutation

Target creature gets +3/+1 and gains lifelink until end of turn. (Damage dealt by the creature also causes its controller to gain that much life.)

Plaguecrafter

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

Swamp

Devouring Swarm

Flying
Sacrifice a creature: Devouring Swarm gets +1/+1 until end of turn.

Gross

Vermin Gorger

{T}, Sacrifice another creature: Each opponent loses 2 life and you gain 2 life.

Witch's Cauldron

{1}{B}, {T}, Sacrifice a creature: You gain 1 life and draw a card.

Thriving Moor

Thriving Moor enters tapped. As it enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

Skullslither Worm

When Skullslither Worm enters, each opponent discards a card. For each opponent who can't, put two +1/+1 counters on Skullslither Worm.