Plasmavore

Plasmavores are a race of alien creatures that exist in the universe of Doctor Who. Though they look human in appearance, they are capable of assimilating the genetic code of other life-forms by consuming their blood, allowing them to fool bio-scanners and pass off as other beings. This is particularly useful to Plasmavores as many of their kind are regarded as criminals across the universe since they have been known to commit brazen acts of murder on different planets.

Known Plasmavores
To date, the only known Plasmavore has appeared in the Doctor Who episode "Smith & Jones". Taking refuge in a London hospital, this Plasmavore - assuming the identity of an elderly woman called Florence Finnegan - was being hunted by intergalactic peacekeepers known as the Judoon for assassinating the Child Princess of Padrivole Regency 9. However, the Judoon had narrowed down her hiding spot and actually abducted the entire hospital, placing it within an atmospheric shell on the Moon so that they could interrogate the patients and staff. Finnegan consumed and assimilated the blood of a doctor, allowing her to pass as human when the Judoon scanned her. She planned to kill everyone with an overpowered MRI scanner and then escape on the Judoon's ship, but she also fed on the Time Lord known as the Doctor, giving her alien genetic material. This allowed the Judoon to recognise her as an alien and they disintegrated her.