Worldwide Recorder Concert - S3-E17
Continuity mistake: In the episode with the recorder concert. When Cartman and Kenny come into the hotel room, saying that they've found the "brown noise", Cartman is wearing headphones and holding another pair in his hand. Then he suddenly has two extra pairs - he gives one to Kyle and one to Stan (and is still wearing one himself).
Worldwide Recorder Concert - S3-E17
Continuity mistake: When the boys are running to stop the concert a frame is seen where Mr Garrison and Mr Macky are saying "are those our boys" and though the previous frame showed the gang of 4 running to the stage. Stan and Kyle's hat can be seen standing next to the teachers.
Answer: He appears in at least 5 other episodes, but usually just as a background character. He can be seen at Cartman's party in "Immaginationland". He was also one of the kids trying out to replace Butters in the "Professor Chaos" episode.
Bishop73