Plasmavore
The Plasmavores were first seen in Smith and Jones (Series 3 : Episode 1), as a race of blood-sucking near-humans, commonly criminals who murdered people across the galaxy and drank their blood. The Plasmavores, though human-like in appearance, are in fact shape shifters. When they drain the blood of an individual, the Plasmavores can mimic the internal structure and the genetic material of their victim, though more extensive mimicry required more feeding. Due to their high salt absorption, the Plasmavores needed blood to survive. While the fed, they would produce exotic plasma energy. Though they required to feed on blood in order to survive, the activity of blood-sucking could become addictive, causing them to develop psychoses and take risks.
The Plasmavores are well known as a dangerous race, travelling the universe looking for new species on which to feed. One Plasmavore, known as Florence Finnegan, murdered and fed in the Child Princess of Padrivole Regency 9 on a whim, resulting in her being hunted by the Judoon. Florence fled to Earth and hid in the Royal Hope Hospital, feeding on the hospitals blood storage. During her time on Earth, she was protected by two Slabs, robotic, typically android; leather clad protectors, though both were destroyed. When the Judoon took the hospital to the Moon, Florence fed on Dr. B. Stoker, and passed as a human on the Judoon's scanning equipment. She then intended to kill everyone using an overpowered MRI scanner. However, she was tricked by the Doctor into drinking his blood, giver Florence his alien genetic material, allowing the Judoon to recognise her as an alien and disintegrate her.