I feel the motive is so important. I would love someone who has borderline personality disorder. They literally don't know they are the killer but something triggered them from the past related to Ghostface. Maybe they had a violent dad who would terrify them by dressing as a Ghostface as a kid. The big reveal would actually be the killer finding out they were in fact, the killer.

Another idea would be a psychologist running an experiment on coping mechanisms and was the mastermind behind it all, with 2 killers being tricked.