Audacious Thief

Whenever Audacious Thief attacks, you draw a card and you lose 1 life.

Sign in Blood

Target player draws two cards and loses 2 life.

Troll of Khazad-dûm

Troll of Khazad-dûm can't be blocked except by three or more creatures.
Swampcycling {1} ({1}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Quag Sickness

Enchant creature
Enchanted creature gets -1/-1 for each Swamp you control.

Corrupt

Corrupt deals damage to any target equal to the number of Swamps you control. You gain life equal to the damage dealt this way.

Rats' Feast

Exile X target cards from a single graveyard.

Tendrils of Corruption

Tendrils of Corruption deals X damage to target creature and you gain X life, where X is the number of Swamps you control.

Crypt Rats

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

Quag Vampires

Multikicker {1}{B} (You may pay an additional {1}{B} any number of times as you cast this spell.)
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
Quag Vampires enters with a +1/+1 counter on it for each time it was kicked.

Dross Golem

Affinity for Swamps (This spell costs {1} less to cast for each Swamp you control.)
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)

Dusk Legion Zealot

When Dusk Legion Zealot enters, you draw a card and you lose 1 life.

Slice from the Shadows

This spell can't be countered. (This includes by the ward ability.)
Target creature gets -X/-X until end of turn.

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.)

Swamp

Defile

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

Trespasser's Curse

Enchant player
Whenever a creature enchanted player controls enters, that player loses 1 life and you gain 1 life.

Seekers' Squire

When Seekers' Squire enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Witch's Cottage

({T}: Add {B}.)
Witch's Cottage enters tapped unless you control three or more other Swamps.
When Witch's Cottage enters untapped, you may put target creature card from your graveyard on top of your library.