X-Men: Apocalypse has hit the big screens and met with mixed reactions from fans. While the film as a whole has been viewed as a success, many criticize the plot holes present in the story. Is one plot hole in particular purposely done to set up for the next film?
Many left confused as to what Apocalypse's power was, but in the film it was stated that he hosted mutants with powers and upon transferring to a new body took the power with him. By the end of the film we witnessed the X-Men beat him both in mind and body. But should their focus have been on his mind alone? Shadow King is hard to define as a character as he has gone through multiple incarnations in the comics, however one trait that always remains is his ability to possess minds. While in possession of a body the eyes of the host would turn black. When Apocalypse transferred bodies or took control of another's mind, the eyes of the victim also turned black.
So Apocalypse could actually be the Shadow King, an entity that passes from host to host to commit their bidding, and explain why his true body and origin is not revealed to the fans in the film. When he discovered a host with mutant abilities he found a way to transfer his mind and the powers along to the next host. When the X-Men defeated his body, stopping him from transferring to Xavier it ended the cycle. This would result in him loosing all his powers he gained as Apocalypse, turning him back to just the Shadow King once again. While this sounds insane and a lot of work just to cover two villains, it would also keep another key X-Men factor canon. Storm was originally manipulated by the Shadow King and not Apocalypse.
This is something that has haunted Storm on more than one occasion in the comics, and it would keep the entity known as the Shadow King key to her origins. The Shadow King also has links to another mutant not yet introduced into the film franchise but is set to be important, Karma.
With the ability to psychically possess others, the young mutant grabbed the attention of the Shadow King due to their similar powers. Why this would make it even more likely for Shadow King to arrive is that Karma is one of the five founding members of the New Mutants, along with Cannonball, Mirage, Sunspot and Wolfsbane. Wolfsbane has already been cast and announced for the film, so would it not make sense to feature the five New Mutants in the next film, ready to spin-off them off into their own film? Perhaps Fox is looking at the bigger picture now, just like Marvel and DC.