When Spectral Arcanist enters the battlefield, it and Drogskol Cavalry trigger.
Resolve the Drogskol Cavalry trigger, causing you to gain 2 life.
Holding priority, 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.
Activate Skirge Familiar by discarding Corpse Dance, adding .
Activate Lord of the Forsaken's first ability by paying and sacrificing Spectral Arcanist, causing target player to mill three cards.
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 hinges on Spectral Arcanist’s ability to repeatedly cast Corpse Dance from your graveyard every time Spectral Arcanist re-enters the battlefield, fueled by the buyback cost paid using mana generated from Lord of the Forsaken. To pull this off, Skirge Familiar acts as the essential outlet to discard Corpse Dance back into the graveyard while converting cards into black mana, which Lord of the Forsaken then transforms into the colorless mana needed for the graveyard restriction. Meanwhile, Drogskol Cavalry sits comfortably on the board as a Spirit to satisfy Spectral Arcanist's requirement while continuously padding your life total and producing the extra Spirit tokens that keep the engine roaring.