Avatar: The Last Airbender Season 2 Episode 16 : Appa's Lost Days
After being abducted, Appa is traded to the Fire Nation Circus where the Circus Trainer mistreats him, though the Sky Bison soon escapes with the help of a small boy. He later unwillingly enters a fight with a Boarcupine, and though wins, is badly wounded. By fortune, Suki and the Kyoshi warriors come across Appa and help him recover from his injuries, but are later attacked by Azula and her team and Appa is forced to flee. He returns to his childhood home at the Eastern Air Temple, where he encounters a mysterious guru. The guru aids Appa in his search for Aang, telling him to find Aang in Ba Sing Se, but before he is able to, he is captured by Long Feng.