The Foretold

The myth of the Foretold grew up around what the Twelfth Doctor identified as an "ancient soldier being driven by malfunctioning tech".

Characteristics
The Foretold was injured in a war and fitted with "state of the art phase camouflage" and a "personal teleporter". The technology within it kept it alive, leading it to kill for over five thousand years, draining the energy from its victims to sustain itself. It remained within the vicinity of a "scroll", which was in fact the flag under which it had fought.

The Foretold killed its victims by moving them out of phase and placing its hands on their temples. The entire process took sixty-six seconds, during which time the victim and only the victim could see and interact with it. The Foretold selected its victims based on physical and mental illness, preying on the weakest first. (TV: Mummy on the Orient Express)

History
The Foretold was brought aboard the space-faring Orient Express, where experts on alien mythology and the sciences had been unwittingly gathered by the computer Gus to study it. The Foretold first killed Mrs Pitt, then a chef, and a guard.

Gus revealed to the Doctor and the passengers the reason why they had been brought together and presented them with a laboratory in which to work. There, the Foretold killed Professor Moorhouse, who was plagued by panic attacks, and Captain Quell, who suffered from post-traumatic stress.

It came for Maisie Pitt, but the Doctor extracted her grief, torment and resentment - the causes of her mental disturbance - and implanted into his own mind. This tricked the Foretold into believing he was Maisie. The Doctor identified it as a soldier and surrendered to it. Freed from its duty, it gave a final salute and disintegrated. (TV: Mummy on the Orient Express)