While I'm not overtly familiar with Buffy, I LOVE the world-building and the effort put into it; makes it feel like I don't HAVE to know about Buffy to ENJOY it. The Crossovers and the Love Spell add a touch of DIVERSITY to the story as well, and Real Life basically turning into M-Rated Fanfiction in that sort of post-event universe makes a great deal of sense. That things like NATIONALITY would begin to disappear on Halloween, even if only in a Minority, would make things tremendously different when NEW races start to crop up, even if THAT facet of it didn't crop up like it did in "Ender in Exile". The part at the END got pretty wild too, though honestly I skimmed over most of THAT since I was only half-familiar with many of the Franchises included.
All in all, a good one-shot. Buffy's Halloween event DEFINITELY leaves wiggle room for wild and wacky crossovers and interactions like this.