Doc Brown created a timeline where Adolf Hitler died in a theatre in 1944 leading to a reality with a population that was far more desensitised to violence, and in that reality they created a fictional shared universe that includes Kill Bill, From Dusk Till Dawn and Sharkboy and Lavagirl.
(Wait a minute...)
Ghostbusters fits in too, since Egon's brother appears in The Earth Day Special. In fact, The Earth Day Special is a composite of many fictional universes. I almost feel like it should take place in the Saturday Night Live universe or something, lol. All this because of two dumb cameos in a very dumb film.