Nightmare Incursion

Search target player's library for up to X cards, where X is the number of Swamps you control, and exile them. Then that player shuffles.

Temporal Extortion

When you cast this spell, any player may pay half their life, rounded up. If a player does, counter Temporal Extortion.
Take an extra turn after this one.

Desecrator Hag

When Desecrator Hag enters, return to your hand the creature card in your graveyard with the greatest power. If two or more cards are tied for greatest power, you choose one of them.

Stalker Hag

Swampwalk, forestwalk (This creature can't be blocked as long as defending player controls a Swamp or a Forest.)

Defile

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

Demon of Death's Gate

You may pay 6 life and sacrifice three black creatures rather than pay this spell's mana cost.
Flying, trample

Extirpate

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Choose target card in a graveyard other than a basic land card. Search its owner's graveyard, hand, and library for all cards with the same name as that card and exile them. Then that player shuffles.

Smogsteed Rider

Whenever Smogsteed Rider attacks, each other attacking creature gains fear until end of turn. (They can't be blocked except by artifact creatures and/or black creatures.)

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Swamp

Cabal Therapist

Menace
At the beginning of your first main phase, you may sacrifice a creature. When you do, choose a nonland card name, then target player reveals their hand and discards all cards with that name.

Drana, Liberator of Malakir

Flying, first strike
Whenever Drana, Liberator of Malakir deals combat damage to a player, put a +1/+1 counter on each attacking creature you control.

Magus of the Coffers

{2}, {T}: Add {B} for each Swamp you control.

Sign in Blood

Target player draws two cards and loses 2 life.

Force of Despair

If it's not your turn, you may exile a black card from your hand rather than pay this spell's mana cost.
Destroy all creatures that entered this turn.