Phineas And Ferb: Season 3, Episode 38

3 - 38:

With Fall around the corner, Phineas and Ferb decide to invent "S'Fall," a colorful world full of giant leaf piles and gourds. Meanwhile, over at Evil Inc., Dr. Doofenshmirtz is mentoring Rodrigo, a budding student of evil. Unfortunately, Rodrigo truly is evil, and when he captures Dr. Doofenshmirtz and Agent P., it's up to Major Monogram's son, Monty, to save the day.