The Eye

The Eye was a hypnotic device invented by Oswald and used by him to seize control of Earth. The Eye could dominate minds or destroy them at higher settings. When Oswald tried to use it against the Third Doctor, the strain overloaded the machine, burning out its circuits. Before he could finish repairing it, the Doctor led the Ancients in rebellion and the boy's power came to an end. (TVC: Children of the Evil Eye)