MEGA-MEGAmind is a giant robot created by Megamind back when he was evil and loaded with his evil personality. It was activated when Megamind, now the defender of Metro City, discovered a box with a button on it. The box was the core of the robot, which contained the robot's brain which loaded itself into it's body upon activation.
The MEGA-MEGAmind mistook its creator for Metro Man and attempted to destroy him. Megamind tried to use his new super suit, which copied Metro Man's powers, to stop him. However this failed miserably. Thanks to a pep talk from Minion, Megamind then used his Spider-bot to lure the robot to the now partially destroyed observatory where it was destroy by Megamind's orbital Death Ray fired by Minion.
It appeared in the animated short Megamind: The Button of Doom