User blog:Bowser & Jr./Phineas and Ferb Crosses a New Dimension Again

Although not a movie, apparently Phineas and Ferb go to another world/dimension again in Doof Dynasty. Phineas and Ferb must save Princess Isabella from the evil Doofus Khan.

Sounds like that ancient Chinese episode they were talking about in that special Phineas and Ferb issue about the movie.