I have a suggestion for your South Park x Reader.
Suggestion: Add The freedom pals or add in the stick of truth.
Stick of truth: The boys let Y/n play in thier game because they need help on something. The elves still don't know where the stick of truth is. (Not Kyle and Jimmy) So, the Elves try to take the stick themselves without a king.
Freedom Pals: Y/n discovered the Freedom pals by getting out numbered by meth heads and 6th graders for pissing them off at night. Freedom Pals swoop in and help Y/n. They introduce themselves and the others, making Y/n fascinated by them and becoming one of those girls that would get in trouble of Super Hero business.