Bubbling Muck

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

Vilis, Broker of Blood

Flying
{B}, Pay 2 life: Target creature gets -1/-1 until end of turn.
Whenever you lose life, draw that many cards. (Damage causes loss of life.)

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

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

Black spells you cast cost {1} less to cast.