19. Nightmare On Elm Street/Evil Dead Crossovers
Across several films, horror legends Wes Craven and Sam Raimi developed a pretty hilarious back and forth.
It all started in the first Evil Dead, which featured a ripped up poster of The Hills Have Eyes in the background of one scene. This is thought to be a joke about a moment in The Hills Have Eyes showing a torn Jaws poster, implying Craven's film was scarier than Jaws. In that case, Raimi was cheekily saying the same about Evil Dead over The Hills Have Eyes.
Craven saw Raimi's tribute and responded in his next movie, A Nightmare on Elm Street. About a half hour in, The Evil Dead is playing on the TV while Nancy is falling asleep which, like Raimi's shoutout, is both a tip of the hat and also kind of a subtle burn, implying the film isn't scary enough to keep someone attentive.
The back and forth continued one more time in Evil Dead II, and when Ash kills his girlfriend with a chainsaw, Freddy's glove is hanging above the door.
To summarize, The Evil Dead references a Craven movie, then a Craven movie references a Raimi movie, and finally a Raimi movie references a Craven movie because a Craven movie referenced a Raimi movie. That is exhausting.