Weeping Angel

The Weeping Angels were an incredibly powerful species of quantum-locked humanoids, so called because their unique nature necessitated that they often covered their faces with their hands to prevent trapping each other in petrified form for eternity by looking at one another. They were known for being "kind" murderous psychopaths, eradicating their victims "mercifully" by dropping them into the past and letting them live out their full lives, just in a different time period. This, in turn, allowed them to live off the remaining time energy of the victim's life. However, when this potential energy paled in comparison to an alternative power source to feed on, the Angels were known to kill by other means, such as snapping their victims' necks.