Activate Krark-Clan Ironworks by sacrificing Iron League Steed, adding ({C} magic symbol) ({C} magic symbol) .
When Iron League Steed dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Iron League Steed from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Iron League Steed enters the battlefield, its fabricate ability triggers, creating a 1/1 Servo artifact creature token.
Activate Krark-Clan Ironworks by sacrificing the Servo, adding ({C} magic symbol) ({C} magic symbol) .