Leaden Myr

Defile

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

Chittering Rats

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

Desolation

At the beginning of each end step, each player who tapped a land for mana this turn sacrifices a land. Desolation deals 2 damage to each player who sacrificed a Plains this way.

Charcoal Diamond

Charcoal Diamond enters tapped.
{T}: Add {B}.

Icequake

Destroy target land. If that land was a snow land, Icequake deals 1 damage to that land's controller.

Rancid Earth

Destroy target land.
Threshold — If seven or more cards are in your graveyard, instead destroy that land and Rancid Earth deals 1 damage to each creature and each player.

Swamp

Gurmag Angler

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)

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.

Smallpox

Each player loses 1 life, discards a card, sacrifices a creature, then sacrifices a land.

Dakmor Salvage

Dakmor Salvage enters tapped.
{T}: Add {B}.
Dredge 2 (If you would draw a card, you may mill two cards instead. If you do, return this card from your graveyard to your hand.)

Despoil

Destroy target land. Its controller loses 2 life.

Rain of Tears

Crowded Crypt

{T}: Add {B}.
Whenever a creature you control dies, put a corpse counter on Crowded Crypt.
{4}{B}{B}, {T}, Sacrifice Crowded Crypt: Create a 2/2 black Zombie creature token with decayed for each corpse counter on Crowded Crypt. (A creature with decayed can't block. When it attacks, sacrifice it at end of combat.)