It's very hard to talk about M. Night Shyamalan movies without bringing in the twist ending. They have become half of the point of his movies, and they also appear to be getting worse as his movies decline. The review for Split didn't spoil the ending, but it is an ending that should be talked about because it fails on so many different levels. This article is not only going to spoil the ending of Split, it is also going to spoil the twist ending that people are going to use to try to justify the rest of the movie. If you don't want to know these spoilers then this isn't the article for you.
The movie doesn't waste too much time revealing that James McAvoy's character is obsessed with sex. For the entire movie he makes the three young women slowly undress. Our heroine, Casey, is wearing the most layers and remained the most clothed by the end. Over the course of the movie we also learn that Casey was molested by her Uncle, starting at a very young age. At one point she is hunting with him and her dad, and she turns a gun on him. However, she doesn't pull the trigger, and by the end we find out that she has to live with him now that her father passed away from a sudden heart attack. While they don't show any graphic molestation, the movie isn't subtle about it, and that combined with the rapey undertones make everything so much worse.
We also find out that James McAvoy's character — his real name is Kevin though we don't find that out until the end — has a twenty-fourth personality that is trying to emerge. This personality is called 'the beast'. We find out that Kevin was abused by his mother and that is why these various personalities begin to emerge. They were protection against the abuse that he was suffering. It's very much implied that this abuse was also sexual. As 'the beast' emerges, Kevin's strength increases and he gains the ability to climb walls. It has never been implied before this moment that there was anything supernatural going on in this movie, so the tonal dissonance does not work. Kevin proceeds to kill his therapist, then mauls and eats the other two girls.
Casey finds a note which says that speaking Kevin's full name will revert him back to his original personality. Kevin tells her to take a shotgun and kill him. However, before she can do this, the beast takes over again. Casey shoots him several times, but it doesn't appear to have any effect on him. She locks herself in a cage with a gun and rips off her last long sleeved shirt so she is only in a tank top. Kevin can see her scars now, they looked as if they could have been self inflicted, and because of that he thinks that she is just as damaged as he is. So he spares her life and leaves her there as he runs off.
She is rescued, eventually, and it's heavily implied that she goes back to her Uncle afterwards, though the movie is ambiguous about it. Kevin runs off and says that he is the next evolution of humanity.
The final scene is in a diner, as the news talks about Kevin escaping. A lady mentions that this is "a lot like that guy in a wheelchair from a few years ago" and the camera cut to Bruce Willis' David Dunn from Unbreakable, thus making the movie part of that universe.
There is a lot to break down here. In my earlier review, I noted that Kevin is very sexual, but the movie takes it to the next level. Casey isn't a strong woman who ends up escaping on her own, Kevin just decides to spare her, and he spares her because she was molested. Her ongoing sexual abuse is the reason that he spares her life; not because of anything she does but because he decides she's damaged like him. Casey had almost no agency to begin with but this strips everything away from her. The movie doesn't even let her tell the police officer about the abuse, or decides that it isn't worth being explicit about.
The fact that this is a sequel to Unbreakable feels like Shyamalan is trying to repeat his own career. The Visit was him crawling back to low budget horror like The Sixth Sense, and now Split is calling back to Unbreakable. The man knows he is falling apart, that he's a joke, and now he's trying to remind us of the two good movies he's ever made (aside from the first half of Signs). The idea of a superhero universe is the thing to do now, so Shyamalan is throwing his own hat into the ring when no one asked for it. Unbreakable worked because we knew it was a world where superheroes and super powers exist. Most of Split was trying to be a horror movie, and the twist ending reeks of a movie that wasn't working and this was the easiest way to try and fix it. It reeks of a movie that would have faded into oblivion without linking it to one of Shyamalan's few good movies.
Split is a mess of a movie that a lot of people are going to justify because they like Unbreakable, but that's not how it works. You don't get to link a bad movie to a good one and expect everything else to get hand waved away. You don't get to excuse a bad movie by claiming it's part of a good universe. Split was a bad movie before we went into that diner and found out it was a sequel to Unbreakable. That twist took a broken movie and shattered it.