Android Assassin

An Android Assassin was an android that could turn invisible, except for some abnormalities in the air when it moved around. They had disintegrator blasters for assassinating their enemies.

During one of his adventures, fifteen android assassins attacked the Doctor, but he used the energy from their blasters to charge a teleport device via his sonic screwdriver and teleport away in nano-seconds before he was disintegrated. As recounted by to Clara Oswald, she used this principle to escape death more than once herself, though she admitted that the Doctor, not one to evade danger with the greatest of success, subsequently ended up in a nest of vampire monkeys. (TV: The Witch's Familiar)

Behind the scenes

 * Although this was an earlier incarnation of the Doctor, the viewers were given the flashback with the Twelfth Doctor, although brief glimpses of the Fourth Doctor and the First Doctor were seen as well.
 * told this story to Clara Oswald, giving an in-universe explanation for the Doctor shown being the Twelfth, as it didn't matter to her, as they were all the Doctor to her. She therefore told Clara to just imagine "the eyebrows" (Twelfth Doctor).