If Aurelia is your commander, choose not to return it to the command zone.
When Aurelia dies, Nim Deathmantle triggers, choose not to pay for the trigger.
Resolve the Savior of Ollenbock trigger from step 1, putting a +1/+1 counter on it.
Savior of Ollenbock's second ability triggers, exiling Aurelia from your graveyard.
Activate Ashnod's Altar by sacrificing Savior of Ollenbock, adding ({C} magic symbol) ({C} magic symbol) .
When Savior of Ollenbock dies, its third ability and Nim Deathmantle trigger.
Resolve the Savior of Ollenbock trigger, returning Aurelia from exile to the battlefield.
Resolve the Nim Deathmantle trigger, causing you to pay ({4} magic symbol) to return Savior of Ollenbock from your graveyard to the battlefield, and attach Nim Deathmantle to it.