When Spectral Arcanist enters the battlefield, it triggers.
Holding priority, activate Skirge Familiar by discarding Corpse Dance, adding .
Activate Lord of the Forsaken's first ability by paying and sacrificing Spectral Arcanist.
When Spectal Arcanist dies, Dross Harvester's second ability triggers, causing you to gain 2 life.
Resolve the Lord of the Forsaken ability, causing target player to mill three cards.
Activate Lord of the Forsaken's second ability twice by paying 2 life, adding CC that can only be spent to cast a spell from your graveyard.
Resolve the Spectral Arcanist trigger from step 2, causing you to pay 2 to cast Corpse Dance from your graveyard with buyback.
Resolve Corpse Dance, returning Spectral Arcanist from your graveyard to the battlefield, and returning Corpse Dance to your hand.
Repeat from step 2.
This intricate loop uses Skirge Familiar to bin Corpse Dance into the graveyard, where Lord of the Forsaken's second ability conveniently provides the colorless mana required to pay for the buyback cost. When Spectral Arcanist enters the battlefield, its triggered ability lets you cast that Corpse Dance right back out of the graveyard without paying its mana value, returning the Arcanist to the battlefield to do it all over again. Lord of the Forsaken also acts as the sac outlet by sacrificing Spectral Arcanist, while Dross Harvester offsets the life payments of the Lord with a steady stream of lifegain every time a creature dies.