Aerilon, Abyssal Blood Mage

Hexproof
As an additional cost to cast black permanent
spells, you may pay X life. Those spells cost {b} less to cast for every 1 life paid this way. This
effect reduces only the amount of Black mana
you pay.
{t}{p/b}{p/b}: Sacrifice a creature. You gain life equal
to its toughness.