Android Assassin

An Android Assassin is an android that can 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, 15 android assassins attacked the Doctor, however 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. (TV: The Witch's Familiar)

Trivia

 * 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.
 * 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).