Swamp

Bone Splinters

As an additional cost to cast this spell, sacrifice a creature.
Destroy target creature.

Vampiric Rites

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

Contagion Engine

When Contagion Engine enters the battlefield, put a -1/-1 counter on each creature target player controls.
{4}, {T}: Proliferate twice. (Choose any number of permanents and/or players, then give each another counter of each kind already there. Then do it again.)

Grief Tyrant

Grief Tyrant enters the battlefield with four -1/-1 counters on it.
When Grief Tyrant dies, put a -1/-1 counter on target creature for each -1/-1 counter on Grief Tyrant.

Blowfly Infestation

Whenever a creature dies, if it had a -1/-1 counter on it, put a -1/-1 counter on target creature.

Trigon of Corruption

Trigon of Corruption enters the battlefield with three charge counters on it.
{B}{B}, {T}: Put a charge counter on Trigon of Corruption.
{2}, {T}, Remove a charge counter from Trigon of Corruption: Put a -1/-1 counter on target creature.

Fume Spitter

Sacrifice Fume Spitter: Put a -1/-1 counter on target creature.

Crumbling Ashes

At the beginning of your upkeep, destroy target creature with a -1/-1 counter on it.

Nest of Scarabs

Whenever you put one or more -1/-1 counters on a creature, create that many 1/1 black Insect creature tokens.

Carnifex Demon

Flying
Carnifex Demon enters the battlefield with two -1/-1 counters on it.
{B}, Remove a -1/-1 counter from Carnifex Demon: Put a -1/-1 counter on each other creature.

Soul Snuffers

When Soul Snuffers enters the battlefield, put a -1/-1 counter on each creature.

Skinrender

When Skinrender enters the battlefield, put three -1/-1 counters on target creature.

Foul-Tongue Shriek

Target opponent loses 1 life for each attacking creature you control. You gain that much life.

Trespasser's Curse

Enchant player
Whenever a creature enters the battlefield under enchanted player's control, that player loses 1 life and you gain 1 life.

Contagion Clasp

When Contagion Clasp enters the battlefield, put a -1/-1 counter on target creature.
{4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Bastion of Remembrance

When Bastion of Remembrance enters the battlefield, create a 1/1 white Human Soldier creature token.
Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life.

Swarm of Bloodflies

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