When Soul Collector enters the battlefield, Pandemonium triggers, causing Soul Collector to deal damage to itself equal to its power.
If an ability from Altar of Dementia is waiting to resolve, let it resolve.
Activate Altar of Dementia by sacrificing Soul Collector.
When Soul Collector dies, it triggers, returning itself from your graveyard to the battlefield.
Repeat from step 2.
This delightfully macabre loop turns Soul Collector's own lethal greed into an endless cycle of recursion. Whenever Soul Collector enters the battlefield, Pandemonium ensures it deals damage to itself equal to its power, setting up its triggered ability to resurrect it the moment it dies. Before that happens, you feed Soul Collector to Altar of Dementia to mill an opponent for its power, triggering the resurrection clause that brings it right back for another round.