Type in the word VORTEX and press and hold the reset button on the machine. After a couple of seconds, an animation sequence with all the cool game robots will show them being sucked into a vortex. This sequence will loop until the reset button is released.
The following codes are all entered at the "NEW NAME" entry screen:
At the "NEW NAME" screen press L
(the button on top of the controller),
C-RIGHT, and C-DOWN to bring up
the secret characters.