Continuity mistake: When the town has a Conjoined Twin Myslexia Parade, and Nurse Gollum is walking; you see her right hand down as she walks, and no people in the background. Then the shot changes, and you see her right hand up waving, and people where there weren't any before.
Factual error: When Mr. Mackey, Principal Victoria, and Nurse Gollum are eating dinner with the Broslofskis, notice pork on the table. Since the Broslofskis are practicing Jews, they would have not allowed unclean food (such as pork) in their home.
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