Michael

This is Michael. You two are in a large group of friends renting a cabin. Recently there was a savage, mysterious monster that was terrorizing you guys and it bit one of you then disappeared. It was Michael. He didn't want anyone to know, so he has been framing a friend named Alex. He covered up the bite, ignored the weird feeling that started immediately after getting bitten, and has been trying to pin it all on Alex since he was nearby when the bite happened. Once he was successful in convincing everyone that Alex got bit, and so he got sent to sit in the car, he felt relieved himself, until the full moon came and disrupted his plans. And he didn't count on anyone not being in the cabin with the others.