Play as Dan
At the title screen, hold Start and press Down, Left(7), then any button to unlock Dan.
Play as Demitri
At the title screen, hold Start and press Right(3), Left, Up, Right, Down, Up, then any button to unlock Demitri.
Play as Evil Lori
At the title screen, hold Start and press Up(3), Down, Left, Right, Down, Left to unlock Evil Lori.
Play as Geese
At the title screen, hold Start and press Left(3), Down, Left, Up, Right, Up to unlock Geese.
Play as Goneitz
At the title screen, hold Start and press Down(3), Right, Down, Left(3) to unlock Goneitz.
Play as Mars Alien
At the title screen, hold Start and press Up, Down, Right(3), Up, Down, Left(2), Down, then any button to unlock Mars Alien.
Play as Violent Ken
At the title screen, hold Start and press Up(2), Down, Left(2), Right, Left, Up, then any button to unlock Violent Ken.
Play as Zero
At the title screen, hold Start and press Up, Right(2), Left(2), Down, Up(3), then any button to unlock Zero.