You control another nontoken nonartifact creature.
Steps
Activate Ashnod's Altar by sacrificing another nontoken nonartifact creature, adding ({C} magic symbol) ({C} magic symbol) .
When the creature dies, Nim Deathmantle and Missy's first ability triggers.
Resolve the Nim Deathmantle trigger, choosing not to pay.
Resolve the Missy trigger, returning the creature from your graveyard to the battlefield face down as a 2/2 Cyberman artifact creature.
Activate Ashnod's Altar by sacrificing the Cyberman, adding ({C} magic symbol) ({C} magic symbol) .
When the Cyberman dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return the creature from your graveyard to the battlefield face up, and attach Nim Deathmantle to it.