S03E34: The Remains of the Platypus

Craziness has ensued in Danville and no one has any idea what’s going on. The wackiness unfolds when Phineas and Ferb create Cheesetopia, Doofenshmirtz makes Perry his butler with his Butler-inator, and Carl is trapped by Doof while in a squirrel costume. All is explained, in an episode of Phineas and Ferb that starts at the end and works its way back to the beginning.