So I've came up with a spinoff to Phineas and Ferb. It's called "Phineas and Ferb... in college!" Here goes:
The spinoff takes place at Tri-State State College. While Phineas is looking around the college, he saw something: a big field with a big tree, just like in the backyard! So, he builds a teleportation machine, which creates a portal to go to the different colleges. First, he starts with Ferb's college — Camford on Oxbury. Ferb comes in through the portal. The same process goes for Baljeet and Buford. However, as soon as Phineas closes the portal, Sir Hortensnyfer (HOR-ten-SNY-fer) sees the portal and says that if Phineas builds something in that field again, he will send Phineas to the principal's office. That makes Sir Hortensnyfer the antagonist of "Phineas and Ferb... in college!".