Play as Kemo Claw:

Highlight "Arcade Mode" and press Left, Left, Left, Right, Right, Right, Left, Right, Left, Right.

Play as Nat Daddy:

First unlock Kemo Claw, then highlight "Arcade Mode" and press Right, Right, Right, Left, Left, Left, Right, Left, Right, Left.

Play as Damien Black:

First unlock Kemo and Nat, then highlight "Arcade Mode" and press Right, Left, Right, Right, Left, Left, Right, Right, Right, Left, Left, Left.