Without his arm to protect him, you're able clang him in the side of the head and throw his balance off his last remaining leg. He falls to the side unable to move.
ATTACK!!!
Left side of his head! Go for the eyes! Right side of his head!
Attack his left arm! Go for his circuits! Attack his right arm!
KICK HIM IN THE BALLS!!!
Take out his left leg! Take out his right leg!