Film Theory: Split Is More Than A Standalone Sequel To Unbreakable...

If we were to take a look at Signs for example, and the representation of aliens as demons that you can explore in this film theory piece, the appearance of these hellish entities could be the beginning of supernatural manifestations in our plane of being - signposting a crossover that could result in the superpowered humans of Unbreakable. Or at least, the terrifying reality of what happens when the supernatural entities informing those with DID become visible to everyone, not just the in-patients.

It makes sense when looking at Devil too, then, that supernaturality is seeded deep into the human psyche, so much so that the very devil himself can take hold of a human host and utilise it for his own puppetry through mental connection.

Devil could also be the reasoning behind the 24th personality itself, a transfiguration of the character into the devil that he can’t control - but unlike the other characters in the elevator movie, because of Kevin’s DID and adjusted mental state of being, he can push the demon out with much more success than others subjected to its will, giving him moments of clarity.

Going further, The Village and The Visit are easily enough slotted into any universe, and The Happening could be an end of days apocalyptic event that allows only the strongest of mind and abilities to survive, making Avatar: The Last Airbender a veritable reality for those inhabiting the earth. It would make sense that these people learned to control the elements to ensure their survival, after all.