Activate Altar of Dementia by sacrificing Reassembling Skeleton.
When Reassembling Skeleton dies, Pitiless Plunderer and Pawn of Ulamog trigger.
Resolve the Pitiless Plunderer trigger, creating a Treasure artifact token.
Resolve the Pawn of Ulamog trigger, creating a 0/1 Eldrazi Spawn creature token.
Resolve the Altar of Dementia ability, causing target player to mill cards equal to Reassembling Skeleton's power.
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .
Activate the Eldrazi Spawn by sacrificing it, adding ({C} magic symbol) .
When the Eldrazi Spawn dies, Pitiless Plunderer triggers, creating a Treasure token.
Activate Reassembling Skeleton by paying ({1} magic symbol) ({B} magic symbol) , returning it to the battlefield from your graveyard.
Repeat any number of times.
Once you have infinite Treasure tokens, you may repeat this loop spending mana from Treasures instead of Eldrazi Spawns in step 7, giving you infinite Eldrazi Spawn tokens.