Play as Inoz
Accumulate over two hours of total game play. Then at the character selection screen, hold L while choosing Mamazo.

Play as Darkness
Accumulate over five hours of total game play. Then, Darkness will be selectable at the character selection screen.

Extra options
Accumulate over ten hours of total game play. Then, an "Extra options" selection will appear on the options menu.

Alternate costume colors
At the character selection screen, press the various Punch and Kick buttons while choosing a fighter.