Nightmare

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

Dread Presence

Whenever a Swamp enters the battlefield under your control, choose one —
• You draw a card and you lose 1 life.
• Dread Presence deals 2 damage to any target and you gain 2 life.

Ob Nixilis Reignited

+1: You draw a card and you lose 1 life.
−3: Destroy target creature.
−8: Target opponent gets an emblem with "Whenever a player draws a card, you lose 2 life."

Go for the Throat

Swamp

Squelching Leeches

Squelching Leeches's power and toughness are each equal to the number of Swamps you control.

Bloodchief's Thirst

Kicker {2}{B} (You may pay an additional {2}{B} as you cast this spell.)
Destroy target creature or planeswalker with mana value 2 or less. If this spell was kicked, instead destroy target creature or planeswalker.

Invoke Despair

Target opponent sacrifices a creature. If they can't, they lose 2 life and you draw a card. Then repeat this process for an enchantment and a planeswalker.

Sign in Blood

Target player draws two cards and loses 2 life.

Phyrexian Rager

When Phyrexian Rager enters the battlefield, you draw a card and you lose 1 life.

Tenacious Underdog

Blitz—{2}{B}{B}, Pay 2 life. (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.)
You may cast Tenacious Underdog from your graveyard using its blitz ability.

Agonizing Remorse

Target opponent reveals their hand. You choose a nonland card from it or a card from their graveyard. Exile that card. You lose 1 life.

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Swift End

Destroy target creature or planeswalker. You lose 2 life. (Then exile this card. You may cast the creature later from exile.)

Murderous Rider

Lifelink
When Murderous Rider dies, put it on the bottom of its owner's library.

Murderous Rider // Swift End

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.

Kalitas, Traitor of Ghet

Lifelink
If a nontoken creature an opponent controls would die, instead exile that card and create a 2/2 black Zombie creature token.
{2}{B}, Sacrifice another Vampire or Zombie: Put two +1/+1 counters on Kalitas, Traitor of Ghet.