In addition to its unusual cast of regular characters, Clay Fighter 63 1/3 also has some nifty hidden characters. All of the following codes are entered at the character selection screen:
To Play As Dr. Kiln
At the character select screen, hold L and press B, Left C, Top C, Right C, Bottom C, A, to release Dr. Kiln.
To Play As Sumo Santa
At the character select screen, hold L and press A, Bottom C, Right C, Top C, Left C, B, to release Sumo Santa.
To Play As Boogerman
At the character select screen, hold L and press Up, Right,Down, Left, Right, Left on the Control Pad, not the Control Stick, to release Boogerman.