User blog comment:Mobo85/Walt Disney Studios Cancels "Phineas and Ferb" Feature Film/@comment-4241330-20130911122537/@comment-1856476-20130911184457

It is not a spinoff, because there is "Phineas and Ferb" banner and it's numer is 436 which means that it is just Season 4's episode. I think that it is just a kind of a joke that the name of the episode sounds like a name of the show or it's an episode about Doof's show.