Baneful Omen

At the beginning of your end step, you may reveal the top card of your library. If you do, each opponent loses life equal to that card's mana value.

Cabal Coffers

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

Cemetery Desecrator

Menace
When Cemetery Desecrator enters or dies, exile another card from a graveyard. When you do, choose one —
• Remove X counters from target permanent, where X is the mana value of the exiled card.
• Target creature an opponent controls gets -X/-X until end of turn, where X is the mana value of the exiled card.

Cloudkill

All creatures get -X/-X until end of turn, where X is the greatest mana value of a commander you own on the battlefield or in the command zone.

Induce Despair

As an additional cost to cast this spell, reveal a creature card from your hand.
Target creature gets -X/-X until end of turn, where X is the revealed card's mana value.

Cabal Stronghold

{T}: Add {C}.
{3}, {T}: Add {B} for each basic Swamp you control.

Cabal Conditioning

Any number of target players each discard a number of cards equal to the highest mana value among permanents you control.

Dread Cacodemon

When Dread Cacodemon enters, if you cast it from your hand, destroy all creatures your opponents control, then tap all other creatures you control.