When Tangled Colony dies, it and Nim Deathmantle triggers.
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Tangled Colony from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Tangled Colony enters the battlefield, Pandemonium triggers, dealing damage equal to Tangled Colony's power to any target.
Resolve the Tangled Colony trigger, creating a 1/1 Rat creature token.
When the Rat enters the battlefield, Pandemonium triggers, dealing 1 damage to Tangled Colony.
Activate Ashnod's Altar by sacrificing the Rat, adding ({C} magic symbol) ({C} magic symbol) .