My Antagonist/Protagonist

I have decided to do something a bit different to normal horror films where there are two main people, the antagonist and the protagonist. I will have both of them in my trailer however, due to the storyline, they are the same person. My plot is similar to a possession as the antagonist is part of the protagonist. The whole thing is sort of a split personality disorder type thing which is the results of experiments done to the protagonist as a child.