Skovox Blitzer

A Skovox Blitzer was a robot built for war, said to be among the most dangerous weapons ever created. A single Blitzer was capable of destroying Earth with it's weaponry. One came to Earth in the early 21st century. The Doctor theorised that is was attracted to the area around Coal Hill School by the high number of artron energy emissions. It was detected by the Twelfth Doctor, who trapped it and projected it into the Time Vortex by using chronodyne generators.

However, as Danny Pink had turned off some of the generators, it was not projected as far into the future as the Doctor had planned. Before it reappeared, he developed a device that would make his orders sound as though they were coming from one of the robots' superiors. With the assistance of Clara Oswald and Danny, he again trapped it, and ordered it to deactivate. He then left it drifting in space and told it to enjoy its war. (TV: The Caretaker)