Activate Ashnod's Altar by sacrificing Tuktuk the Explorer, adding ({C} magic symbol) ({C} magic symbol) .
Tuktuk the Explorer dies, triggering itself and Nim Deathmantle.
Resolve the Tuktuk the Explorer trigger, creating a 5/5 Tuktuk the Returned artifact creature token.
Activate Ashnod's Altar by sacrificing Tuktuk the Returned, adding ({C} magic symbol) ({C} magic symbol) .
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Tuktuk the Explorer from your graveyard to the battlefield, and attach Nim Deathmantle to it.