Cast Peer into the Abyss by paying ({4} magic symbol) ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) , causing an opponent to draw cards equal to half their library size and lose half their life total, rounded up.
Sheoldred's second ability triggers for each card drawn this way.
Resolve the first Sheoldred trigger, causing the opponent to lose 2 life.
Repeat step 3 until the opponent loses the game due to having zero or less life.