Jugan dies, triggering itself and Nim Deathmantle.
Resolve the Jugan trigger, putting five +1/+1 counters on Crystalline Crawler.
Activate Crystalline Crawler's first ability three times by removing three +1/+1 counters from it, adding ({3} magic symbol) .
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Jugan from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to Jugan's power.
Repeat.
Results
Infinite +1/+1 counters on all creatures you control except Jugan.