After the events of the Harmonic Convergence, numerous portals leading to various dimensions sprout out of nowhere. Korra and her team inadvertently end up helping Phineas and Ferb in rescuing Perry from the clutches of the evil Dr. Doofenshmirtz. MAJOR SPOILERS FOR "Across the Second Dimension" AND "Book 2: Spirits" INSIDE! READ AT YOUR OWN RISK! ALL SHOWS BELONG TO THEIR OWNERS.