When Rainbow Dash's pranking gets out of hand, the other ponies decide to give her a taste of her own medicine. However, Doofenshmirtz's latest "-inator" accidentally turns the ponies of Ponyville into contagious mindless replusive cookie-craving zombie ponies who run rampant all over Danville. Phineas, Ferb, Perry and the gang must work together and avoid becoming mindless replusive cookie-craving zombie ponies themselves.