Spectre

Spectres are humanoid constructs formed from thousands of nano-machines serving as a combat unit by the Ethereals during their occupation of Earth. Although they are composed of a swarm of nano-machines, Spectres typically maintain a humanoid shape and usually dissolve into a cloud-like form when traversing short distances. Along with their apparent skill in handling rifles and evading incoming fire, Spectres are also capable becoming temporarily invisible and draining vitality from their enemies. Perhaps their most notable combat ability, known as 'shadowbound', is to render a humanoid lifeform (as demonstrated on Humans) unconscious and create a copy of the victim from their own nano-machines. The copy will be under the apparent control of the Spectre, displaying complete reliance on it to maintain its form, and will mimic the equipment, weaponry and abilities of its host.

Interestingly, Spectres will retain their humanoid form even after death. This implies the possibility that the nano-machines are connected via magnetism. Despite their robotic nature, Spectres cannot be hacked and controlled by external forces.