Play as Anil 8
At the character select screen press Up,
Right, Down, Right, Right, Up, Left,
Up.
Submitted by Robert Knickerbocker

Play as Assault
At the character select screen, press Right,
Up, Up, Right, Down, Right, Up, Up.

Play as Mayhem
At the character select screen, press Left,
Right, Down, Left, Up, Left, Down,
Left, Down.

Play as Supervisor
At the character select screen press Down,
Right, Down, Up, Right, Down, Left,
Down, Up, Right, Up.
Submitted by Robert Knickerbocker

Play as Vitriol
At the character select screen, press Left,
Left, Left, Up, Up, Down, Left, Left,
Down, Down.