The Remains of the Platypus, Mom's In the House

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.
When Phineas and Ferb can’t find Perry, they decide to create the Perrytronic 3000, a mechanical structure that can assume any form. Of course, being aware of the boys’ every move, Candace decides to take a different tactic on her busting approach by using a new technique that keeps Phineas and Ferb from finishing their Perry project. Meanwhile, Doofenshmirtz invents a Duplicator-Inator-2 so that he can duplicate his own head and make himself twice as smart.