The Strangers
The Strangers is based on the real Keddie Cabin murders (even though the director has never said so, it's glaringly obvious). A group of people break into a cabin and begin to wreak havoc on a family. They wear masks the entire time, which only dehumanizes these people and makes them even scarier.
Kevin Wendell Crumb - James Mcavoy
James Mcavoy was basically playing multiple characters at once. Kevin Wendell Crumb is a man who has multiple personalities that he can't control. The most threatening character is The Beast, who has superhuman strength and takes this film into the supernatural realm.