The Sentience (Nightshade)

The Sentience was an ancient and powerful force that lived inside the Earth, focused under Crook Marsham.

Biology
The Sentience took the form of a mass of energy. Most of its body was located under a hill at Crook Marsham, but it was able to send out tendrils that looked like columns of energy in order to feed.

The Sentience fed on energy, including those of Humans. It can't feed on Humans directly and instead need to latch on to strong memories, such as regrets and desires. The Sentience will then create copies of the focus of these memories and try to interact with the target. The stronger the belief in the memories is, the more powerful the copy is and the easier the Sentience can feed. After coming into contact with the target, the Sentience will feed on all the energy of the Human, leaving a dessicated corpse that will disintegrate with a touch.

The Seentience also developed other powers to help it feed. It could cut off all telephone lines around Crook Marsham, stopping the inhabitants from calling for help. It was able to possess Billy Coote, but the energy eventually destroyed him. It could set up a forcefield that would make anyone who tried to escape sick and fearful. As it grew in power, it could also leave Earth and travel through time and space at great speeds. (NA: Nightshade)

History
The Sentience was present during the creation of Earth and was trapped inside the planet as it formed. For billions of years, the Sentience was too weak to react much. The low population in the area meant that there was little for it to feed on.

In 1968, a radio telescope was built on top where the Sentience was. This increase in both population and energy awoke the Sentience, and it started to feed on the inhabitants of Crook Marsham. It was eventually confronted by the Doctor, who showed it the energies given off by Bellatrix going nova. The Sentience followed the fossil energies back through time to 1644, destroying the castle of Crook Marsham along the way. It then went to a supernova in the Andromeda Galaxy, but was trapped when it turned into a black hole. (NA: Nightshade)