Ponyback Brigade dies, triggering Nim Deathmantle, causing you to pay ({4} magic symbol) to return Ponyback Brigade from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Ponyback Brigade enters the battlefield, creating three 1/1 Goblin creature tokens.
Activate Skirk Prospector three times by sacrificing the Goblins, adding ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .