A very impressive fan fiction piece. Just a couple things- Stan rarely talks so much or acts so weird in South Park. Typically I think Butters talks more and acts weird. Also, it's important to change up the target of the show. South Park never just goes after one target- usually there are multiple things in it they are making fun of.

From an animation standpoint, nothing I would change. From a voice acting standpoint, your options are limited without matt stone and trey parker. But Cartman's voice was right on the money.

From a story standpoint it was fairly cohesive and made fun of itself, which is typical with South Park.

Given the materials you had at your disposal, this was very well executed. Good work