Aether Channeler dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Aether Channeler from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Aether Channeler enters the battlefield, creating a 1/1 Bird creature token.
Activate Ashnod's Altar by sacrificing the Bird, adding ({C} magic symbol) ({C} magic symbol) .