When Ferocious Pup dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Ferocious Pup from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Ferocious Pup enters the battlefield, it triggers, creating a 2/2 Wolf creature token.
Activate Ashnod's Altar by sacrificing the Wolf, adding ({C} magic symbol) ({C} magic symbol) .