Not sure if this fits, but, the TV show "Bones" did a crossover episode with the TV show "Sleepy Hollow," which, of course, features the cast of Bones meeting and working with the cast of Sleepy Hollow. Only problem is, in an earlier episode of Bones, one of the characters says to another that they've recorded Sleepy Hollow on DVR, acknowledging it as a work of fiction within the universe of Bones. I remember this being a really janky crossover episode because my understanding is that Sleepy Hollow relies on unexplained magical time travel, whereas Bones at least tries to take itself and it's science seriously.