The second, more plausible explanation is that a very dead Jason has a twin running around Riverdale. Jason comes from a long line of twins, and as far as we know is a twin himself, with sister Cheryl (Madelaine Petsch). Perhaps Jason and Cheryl are really triplets, and Jason and his brother are identical. It's also possible that this twin is really the one who was murdered by Cliff, and that Jason is actually the Gargoyle King, as Ethel revealed.