If you loved Phineas and Ferb the Movie: Candace Against the Universe, try Phineas and Ferb The Movie: Across the 2nd Dimension
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.

Phineas and Ferb the Movie: Candace Against the Universe

Phineas and Ferb The Movie: Across the 2nd Dimension
What they share
Both films are directed by Dan Povenmire, and they both carry the cozy, playful mood tags, and they sit in Animation / Comedy / Family / Science Fiction territory. If that's the register that drew you to Phineas and Ferb the Movie: Candace Against the Universe, the second film will land in a comparable space — through a different lens.
What Phineas and Ferb The Movie: Across the 2nd Dimension is
The multiverse: still having its moment. Phineas and Ferb travel to a parallel dimension where Doofenshmirtz is in charge, which is bad news for everyone. Luckily, Perry the Platypus is also on hand, living a double life as a secret agent. A solid afternoon's work.