Midnight entity

The Midnight entity was the term given to an unidentified lifeform of unknown origin encountered on the planet Midnight. It was one of the few beings that the Doctor had no knowledge of at all, which, given his expansive, encyclopaedic knowledge of the universe and everything in it across time, was a testament either to its obscurity, or its extraneousness. The creature was never given a name, nor did it display any other form.

Biography
During the Crusader Tours to the Sapphire Waterfall, a tour bus had apparently broken down. While looking out a window, one of the drivers noticed a shadow among the diamonds that was moving far in the distance, "running" towards them.

Following the beginning of the passengers' paranoia, the entity knocked twice around the bus to get everyone's attention. When Mr. Kane and the Doctor knocked a different number of times, the entity mimicked the pattern exactly. Following Sky Silvestry's hysterical blathering, the entity closed in on her from the outside and somehow entered the shuttle without any sign of a hole, while ripping off the cockpit, killing the drivers. In the following blackout from the loss of the main generator, the entity chose to possess Sky. The entity seemed to gather the strength of its host and then repeated every word a person said in exact precisions, including the square root of Pi to 30 decimal places. Eventually, the entity copied word-for-word at the exact same time, focusing on the Tenth Doctor, and eventually stealing his voice, paralyzing him and forcing him to repeat after her. Taking advantage of the hysterical level of paranoia that was already amongst the passengers, the entity convinced them that the Doctor was now possessed and needed to be thrown off the bus. However, while Professor Hobbs and Mr Kane were trying to get rid of the Doctor, the entity made a grave mistake- it began using phrases that the Doctor had previously said, prompting the attention of only the Hostess. The entity was helpless as the Hostess sacrificed herself to drag it out into the Xtonic light, vaporising both of them to free the Doctor from its grip and to ensure the safety of the passengers.

Despite this, the Doctor had no idea if this killed the entity or if there were more. (DW: Midnight)

Powers and abilities

 * The full extent of the entity's power is unknown. Indeed, it is unknown exactly how many of the events in the episode the entity was directly responsible for. It is also unknown whether the entity is part of a species, or existed alone on the planet.

The Midnight entity was capable of surviving on the planet Midnight, despite the fact that the Xtonic rays should have killed any being on the surface, meaning it was a conciousness alone with high telepathic powers. It was capable of shaking a Crusader 50 bus, causing dents in its walls and ripping off the cockpit, such a feat would require great strength. The entity was not very big, as a the shadow seen by mechanic Claude did not attract the attention of the Doctor, but when it began running towards the bus, it had grown in size.

The Midnight entity could also possess a human. It would start to copy what the people around it said, then speak at the same time and then predict what people would say. The Tenth Doctor believed it was trying to learn about its surroundings. The being seemed to be able to learn at an incredibly rapid pace and absorbed the passengers’ speech without forgetting, hesitating, or making a single mistake. As the inhabitants of the ship turned on the Doctor, the entity singled him out as a target. It then paralysed him and forced him to copy the entity's speech, "stealing his voice". It also mimicked his mannerisms, such as his use of pidgin Italian and French, ("molto bene" and "Allons-y").

The entity within Sky also said, more to itself than the others, that that's how it "does it - makes you fight", indicating that the xenophobia and paranoia was at least partially caused by the creature. The rest of the passengers seem to immediately relax once Sky and the Hostess had been dragged outside, though this might have been merely of the shock of seeing the two of them die.

It is implied that the Entity wanted the Doctor's body to die, as it goaded the rest of the passengers into throwing him out of the ship. It is unknown what would have happened had the Doctor died and what the Entity would have gained other than his voice. (DW: Midnight)

Behind the scenes

 * This is the first time on Doctor Who where the true nature of an enemy has never been revealed. The name of the creature is not revealed in the episode, and "Midnight entity" is just an unofficial name.
 * The entity seems almost identical to the species in the Doctor Who Unbound audio drama A Storm of Angels, right down to the gemstone planet it inhabited.