Full Moon (2008)

Russ has invited his niece Allie over even though there's a full moon. He secretly locks himself in his room upstairs and chains up in anticipation of his wolfman transformation. However, he becomes strong and breaks through the chains after he wolfs out. Allie hears some noise upstairs and becomes suspicions. She begins to head up to check on Russ. He leaves through the window and prowls outside before returning. Russ attacks Allie in the kitchen. She grabs a knife and kills him in self defense. Russ collapses, and Allie mourns over the body. If only Russ remembered it was a full moon before offering to babysit.