Activate Ashnod's Altar by sacrificing Old One Eye, adding ({C} magic symbol) ({C} magic symbol) .
Old One Eye dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Old One Eye from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Old One Eye enters the battlefield, it triggers, creating a 5/5 Tyranid creature token.
Activate Ashnod's Altar by sacrificing the Tyranid, adding ({C} magic symbol) ({C} magic symbol) .