Little Magic (Game Boy Color)
On the title screen, press A 10 times and B 10 times in any order, then press Select. A number will appear in the bottom right corner of the screen. Toggle it with Left and Right, and play sounds with A.
Stored at x4044 are a version number for the game's sound driver and credits for a few programmers:
SOUND DRIVER Ver.2.0 PROGRAM T.SAKAI ADVICER JAMI CONVERTER K.TAKAHASHI
Similar text can also be found in other Game Boy Color games by Altron.