When Tithe Taker dies, its afterlife ability and Nim Deathmantle trigger.
Resolve the Tithe Taker trigger, creating a 1/1 Spirit creature token.
Activate Ashnod's Altar by sacrificing the Spirit, adding ({C} magic symbol) ({C} magic symbol) .
Resolve the Nim Deathmantle trigger from step 2, causing you to pay ({4} magic symbol) to return Tithe Taker from your graveyard to the battlefield, and attach Nim Deathmantle to it.