The Succubus (a.k.a. Chef's Mama) - S3-E3
Other mistake: Cartman says, "What? What happened you guys? Is Kenny okay?" The bandages only covered his eyes, not his ears, so even if he's blinded by his bandages, he still should have been able to hear Stan shouting, "Oh my God! She killed Kenny!" and Kyle's reply "You bastard!"
Cat Orgy (1) - S3-E7
Continuity mistake: When Shelly and Skyler are on the couch kissing, Skyler's guitar is on the couch. Then Cartman quickly snaps a picture of them, and then only a second later, the guitar is suddenly on the floor without enough time for it to be moved.
Hooked on Monkey Fonics - S3-E12
Continuity mistake: When Mark rolls into the class in his bubble, he hits Craig's desk and Craig looks annoyed at him. In the next shot, he isn't looking annoyed. (00:08:05)
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