Endrek Sahr and Phyrexian Altar on the battlefield.
You have not completed Tomb of Annihilation.
({2} magic symbol) ({B} magic symbol) available.
Steps
Cast Acererak the Archlich.
Endrek Sahr triggers, creating three 1/1 Thrull tokens.
Acererak the Archlich enters the battlefield and triggers, returning Acererak the Archlich to your hand and venturing into the Lost Mine of Phandelver.
Each time your trigger the Dark Pool room ability, each opponent loses one life and you gain 1 life.
Activate Phyrexian Altar three times by sacrificing a Thrull token each time, adding ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .