You have at least three other cards in your graveyard.
({2} magic symbol) ({B} magic symbol) available.
Steps
Cast Priest of Gix from your graveyard for its escape cost by paying ({2} magic symbol) ({B} magic symbol) and exiling three other cards from your graveyard.
Priest of Gix enters the battlefield, adding ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Activate Lord of the Forsaken's first ability by paying ({B} magic symbol) and sacrificing Priest of Gix.
Priest of Gix dies, triggering Dross Harvester, causing you to gain two life.
Resolve the Lord of the Forsaken ability, causing you to mill three cards.
Activate Lord of the Forsaken's second ability by paying 1 life, adding ({C} magic symbol) that can only be spent to cast spells from your graveyard.