Ah, yes, that episode would be: La Candace-Cabra
Phineas and Ferb set out to prove the existence of the elusive Chupacabra to the world.
Meanwhile, Doofenshmirtz builds a Switch-Place-Inator to remove hair from one person and give it to another so that he can sell his hair growing tonic.
Lol, I'm so glad I saw the Season 2 finale back of Xiaolin Showdown as a rerun and not on its original airdate.
The original gap from Season 2 to Season 3 was from May to September.
Being left on this cliffhanger would've driven me nuts. xD