The fourth and final season of Phineas and Ferb first aired on Disney Channel on December 7, 2012, and December 31, 2012, for Disney XD. The season features two step-brothers trying to make every day the best day ever, while their sister tries to bust them. The five main characters are: brothers Phineas Flynn and Ferb Fletcher, the brothers' older sister Candace Flynn, secret agent Perry the Platypus (who's also the pet of Phineas and Ferb) and the evil scientist Dr. Heinz Doofenshmirtz.