The Tooth Fairy's TATS 2000 - S4-E1
Other mistake: Cartman is excited because the "tooth fairy" left him two dollars in exchange for a tooth. When he holds up the two bills, they are identical. Both have the same serial number.
South Park (1997)
1 other mistake in season 4 - chronological order
Starring: Trey Parker, Isaac Hayes, Matt Stone, Mona Marshall
Woodland Critter Christmas - S8-E14
Continuity mistake: The narrator says that it's "Christmas Eve day," but then the abortion doctor says that it's "three days until Christmas."
Cartman Gets an Anal Probe - S1-E2
Cartman: How come everything today has involved things either coming in or going out of my ass?
Question: Forgot the episode and the season, but does Mark, the kid that gets home schooled and ends up beating Kyle, ever show up in later episodes?
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