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 Viscera Seer ability from step 1, causing you to scry 1.
Repeat.
.
Results
Infinite +1/+1 counters on all creatures you control except Jugan.