Sickening Dreams

As an additional cost to cast this spell, discard X cards.
Sickening Dreams deals X damage to each creature and each player.

Conqueror's Flail

Equipped creature gets +1/+1 for each color among permanents you control.
As long as this Equipment is attached to a creature, your opponents can't cast spells during your turn.
Equip {2}

Dark Ritual

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.

Feast of Sanity

Whenever you discard a card, this enchantment deals 1 damage to any target and you gain 1 life.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Sacrifice

As an additional cost to cast this spell, sacrifice a creature.
Add an amount of {B} equal to the sacrificed creature's mana value.

Faerie Dreamthief

Flying
When this creature enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
{2}{B}, Exile this card from your graveyard: You draw a card and you lose 1 life.

Imp's Mischief

Change the target of target spell with a single target. You lose life equal to that spell's mana value.

Swamp

Sol Ring

Bubbling Muck

Until end of turn, whenever a player taps a Swamp for mana, that player adds an additional {B}.

Bog Initiate

Profane Tutor

Suspend 2—{1}{B} (Rather than cast this card from your hand, pay {1}{B} and exile it with two time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)
Search your library for a card, put that card into your hand, then shuffle.

Insatiable Avarice

Spree (Choose one or more additional costs.)
+ {2} — Search your library for a card, then shuffle and put that card on top.
+ {B}{B} — Target player draws three cards and loses 3 life.

Blood Pet

Culling the Weak

As an additional cost to cast this spell, sacrifice a creature.
Add {B}{B}{B}{B}.

Ugin's Conjurant

This creature enters with X +1/+1 counters on it.
If damage would be dealt to this creature while it has a +1/+1 counter on it, prevent that damage and remove that many +1/+1 counters from this creature.

Death Cultist

Sacrifice this creature: Target player loses 1 life and you gain 1 life.

Varragoth, Bloodsky Sire

Deathtouch
Boast — {1}{B}: Target player searches their library for a card, then shuffles and puts that card on top. (Activate only if this creature attacked this turn and only once each turn.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Rain of Filth

Until end of turn, lands you control gain "Sacrifice this land: Add {B}."

Memnite

Endless One

This creature enters with X +1/+1 counters on it.

Ornithopter

Slaughter Pact

Destroy target nonblack creature.
At the beginning of your next upkeep, pay {2}{B}. If you don't, you lose the game.

Dark Sphere

{T}, Sacrifice this artifact: The next time a source of your choice would deal damage to you this turn, prevent half that damage, rounded down.

One with Nothing

March of Wretched Sorrow

As an additional cost to cast this spell, you may exile any number of black cards from your hand. This spell costs {2} less to cast for each card exiled this way.
March of Wretched Sorrow deals X damage to target creature or planeswalker and you gain X life.