Resolve Orah's trigger, returning any Cleric card with mana value 3 or less from your graveyard to the battlefield.
With Nim Deathmantle's trigger still on the stack, activate Ashnod's Altar by sacrificing the returned Cleric, adding ({C} magic symbol) ({C} magic symbol) .
Resolve the Nim Deathmantle trigger, paying ({4} magic symbol) to return Orah from your graveyard to the battlefield and attach Nim Deathmantle to them.
Repeat.
Results
Infinite blinking of Clerics with mana value 3 or less.