DX Bakenou Z [Model DMG-DZJ]

Secret message:
Any time during the game, press and hold A + B + Select + Start (the Soft Reset code), while holding these buttons, press and hold Left for about a half of the second then release all buttons at once. Now, after the game boot up, in the main menu, enter 5th option (SYSTEM), then 4th (SOUND TEST). The developers logo will appear at the top-left corner of the screen.

Credits:
Any time during the game, press and hold A + B + Select + Start as described above, but press and hold Right for a half of second. Release all the buttons and at exactly the same moment press Select. This may be tricky, keep trying. If done right, the credits scroll will follow immediately.