A friend of mine has found this music in a Japanese Sonic CD Iso (Mega CD version) through Goldwave 5.18

http://rapidshare.com/files/122353653/soniccd.rar.html

Is it completly unused or is just a messed final game music?

Hey there. It actually isn't -completely- unused, but it is unused in this form. This'd be one of the SCDBNK files on the disc -- these typically store the sound samples for the Past versions of the stages. However, there are also very incomplete Present and Future versions of songs, as well. Think of them as test-run samples. This sound sample specifically is from the boss music. It's sorta well known, [i]I think.[/] Don't quote me on that, I'm out-of-date.

I don't have a link offhand, but I believe ICEKnight's page goes much further into depth, with full MP3s of the incomplete songs.

Yes, I remember SCDBNK files, but I can't find one that resemble that music.

SNCBNKB1. That'd be it -- the sampling rate on the extracted sound files is just completely wrong.
Check the pack: http://sost.emulationzone.org/sonic_cd/moozic/index.htm

Beat again, but here is the cult page with the music divided into zone names http://www.sonic-cult.org/dispart.php?cati...d=1&artid=2

If my site was still up... =|