Prowling Geistcatcher | Pawn of Ulamog | Shambling Ghast

(and two other cards)

Activate
Altar of Dementia four times by sacrificing
Cadaver Imp,
Shambling Ghast,
Pawn of Ulamog and another nontoken creature.
Pawn of Ulamog and Prowling Geistsnatcher trigger four times each, and
Shambling Ghast triggers once.
Resolve the
Shambling Ghast trigger, creating a Treasure token.
Resolve all
Pawn of Ulamog triggers, creating four 0/1 Eldrazi Spawn creature tokens.
Resolve all Prowling Geistsnatcher triggers, exiling the sacrificed creatures.
Resolve all
Altar of Dementia abilities, causing target player to mill cards equal to the sacrificed creatures' powers.
Activate
Altar of Dementia by sacrificing Prowling Geistsnatcher.
Prowling Geistsnatcher leaves the battlefield, returning all cards exiled with it to the battlefield.
Cadaver Imp enters the battlefield, returning Prowling Geistsnatcher from your graveyard to your hand.
Resolve the
Altar of Dementia ability from step 7, causing target player to mill cards equal to Prowling Geistsnatcher's power.
Activate three Eldrazi Spawn tokens by sacrificing them, adding ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) .
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .
Cast Prowling Geistsnatcher by paying ({3} magic symbol) ({B} magic symbol) .
Repeat.