Phineas and Ferb - Season 3 Episode 4
Last Train to Bustville

While visiting their grandparents, the kids decide to create and race a giant hot air balloon. Meanwhile, Candace is inspired by train engineer Glendas can-do attitude and decides to "give up" on busting her brothers. On the other side of town, Dr. Doofenshmirtz finds a Dodo bird egg and is convinced that it is a fierce bird-monster that can help him take over the Tri-state area, but discovers the exact opposite when the egg hatches.