Clay Fighter 63 1/3: Sculptor's Cut 

Programmer's mode 
At the character selection screen:
hold L and press A, B, A, B, A, B, C-Left, C-Right, C-Up, C-Right, C-Left, C-Right.
In this mode, any character can be selected, and has an overhead view of each stage.

CPU control 
At the character selection screen:
hold L and press A(5), C-Up, C-Down, C-Left, C-Left, B, A, C-Right.

Play as Boogerman 
At the character selection screen:
hold Z and press B(2), C-Right(2), C-Left(2). 
If you entered the code correctly, you will hear a sound. Then, highlight the "?" box and press R.

Play as Earthworm Jim 
At the character selection screen:
hold Z and press B, C-Left , C-Up , C-Right , C-Down , C-Up.
If you entered the code correctly, you will hear a sound. Then, highlight the "?" box and press R.

Play as High Five 
At the character selection screen:
hold Z and press C-Up, C-Down, C-Left, C-Right, B, A.
If you entered the code correctly, you will hear a sound. Then, highlight the "?" box and press R.

Play as Sumo Santa 
At the character selection screen:
hold Z and press A, C-Right, A, C-Right, C-Down, C-Up.
If you entered the code correctly, you will hear a sound. Then, highlight the "?" box and press R.

Alternate character color 
At the character selection screen:
highlight a fighter and press C-Down.

Random character 
At the character selection screen:
press L + R.