Have

Swamp

Crypt Rats

{X}: This creature deals X damage to each creature and each player. Spend only black mana on X.

Bone Picker

This spell costs {3} less to cast if a creature died this turn.
Flying, deathtouch

Gray Merchant of Asphodel

When this creature 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.)

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Sign in Blood

Target player draws two cards and loses 2 life.

Cast Down

Chainer's Edict

Target player sacrifices a creature of their choice.
Flashback {5}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Diabolic Edict

Target player sacrifices a creature of their choice.

Phyrexian Rager

When this creature enters, you draw a card and you lose 1 life.

Chittering Rats

When this creature enters, target opponent puts a card from their hand on top of their library.

Thorn of the Black Rose

Deathtouch
When this creature enters, you become the monarch.

Blood Fountain

When this artifact enters, create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")
{3}{B}, {T}, Sacrifice this artifact: Return up to two target creature cards from your graveyard to your hand.

Cuombajj Witches

{T}: This creature deals 1 damage to any target and 1 damage to any target of an opponent's choice.

Defile

Target creature gets -1/-1 until end of turn for each Swamp you control.

Witch's Cottage

({T}: Add {B}.)
This land enters tapped unless you control three or more other Swamps.
When this land enters untapped, you may put target creature card from your graveyard on top of your library.