These time-sensitive alien killers are as old as the universe. They send their victims back in time just by touching them, and the Angels feed on the potential time energy created by the vanished people's lives being disturbed.
Often called the Lonely Assassins because they can never touch anything without sending it back in time, they can only move and attack if they are not being observed. If they are seen, they immediately become quantum locked and freeze into solid rock—the ultimate defense mechanism.
Additionally, they have been known to take over their adversaries by entering through their eyes when looked upon, staying in the memory and taking over the victim's mind.