Culling the Weak

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

Lotus Petal

{T}, Sacrifice this artifact: Add one mana of any color.

Maralen of the Mornsong

Players can't draw cards.
At the beginning of each player's draw step, that player loses 3 life, searches their library for a card, puts it into their hand, then shuffles.

Dark Ritual

Boseiju, Who Shelters All

Boseiju enters tapped.
{T}, Pay 2 life: Add {C}. If that mana is spent on an instant or sorcery spell, that spell can't be countered.

Swamp

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.

Sickening Dreams

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