A Very Crappy Christmas - S4-E17
Continuity mistake: When Kyle tells Mr. Hankey and his family about the $300 he got for the animated Christmas card, the olive stick in the wife's martini glass is facing to the right. When she says to Mr. Hankey "That's not the only thing we've got to get working again if you know what I mean", the olive stick in the martini glass is now facing to the left. The olive stick then returns to facing to the right for the remainder of the scene. (00:07:50)
A Very Crappy Christmas - S4-E17
Continuity mistake: Cartman is already on stage, but in a next shot he arrives and Stan and Kyle ask him what he's you doing there. (00:16:58)
A Very Crappy Christmas - S4-E17
Audio problem: The animated Christmas movie the boys are making is really "the Spirit of Christmas", the movie Trey Parker and Matt Stone made before South Park. The dialogue recorded by the boys is the same as in the original (with a few changes, but when the film is shown later it's the original speech from "The Spirit of Christmas". You can tell by the way the voices are done, and the tone of the voices.
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