Seriously now. I'm not trying to be rude, but what is this story? I haven't heard of it, and I'm convinced its fanfiction. I don't think we should have a category for it. I'm not an admin or mod, so maybe I'm wrong. However, please stop. If you think this category is valid, please talk to the admins about it; but for now, I don't believe it is. I don't think this story exists, and even if it does, I'm not sure it's worth making a category for.
It certainly wouldn't be worth a category even if it was a canonical story. That's not how we do categories. But as for what it could possibly be, at a guess, TheMidgetMouse, I would say it's probably one of these YouTube videos where they "create" a "new crossover film" by matching clips of various characters to the audio of a preexisting movie.
That's what I was thinking. We don't have a Christmas on Bear Mountain characters category. My assumption was that is was something from the Idea Wiki or something like that, but I wanted to give the user who repeatedly added categories about it the chance to explain.