Activate Krark-Clan Ironworks by sacrificing Cathodion, adding CC.
Cathodion and Nim Deathmantle trigger.
Resolve the Cathodion trigger, adding CCC.
Resolve the Nim Deathmantle trigger, causing you to pay 4 to return Cathodion from your graveyard to the battlefield, and then attach Nim Deathmantle to it.