Play as the following bosses by entering the corresponding codes at the character selection screen:

BOSS - CHEAT CODE
Anil 8 - UP, RIGHT, DOWN, RIGHT, RIGHT, UP, LEFT, UP
Assault - RIGHT, UP, UP, RIGHT, DOWN, RIGHT, UP, UP
Mayhem - LEFT, RIGHT, DOWN, LEFT, UP, LEFT, DOWN, LEFT, DOWN
SUPervisor - DOWN, RIGHT, DOWN, UP, RIGHT, DOWN, LEFT, DOWN, UP, RIGHT, UP
Vitriol - RIGHT, RIGHT, RIGHT, UP, UP, DOWN, LEFT, LEFT, DOWN, DOWN