The Monster of Phineas-n-Ferbenstein

A rainy day causes Phineas and Ferb to cancel today's activities. To pass the time, Grandpa Reg tells the story about one of Ferb's Victorian ancestors, Ferbgor, who helped a scientist, Dr. Phineastein, create a monster. While locked in his own building, Heinz Doofenshmirtz tells Agent P the story about his ancestor, Jeykll Doofenshmirtz, who made a concoction brewed to turn him into a monster.