If you check the Super Paper Mario video on the Nintendo Channel, the sounds are a little different. Now, I'm NOT sure that it's a prototype or not, but if it is, then it's REALLY close to being finished. I also hypothesize that it may be a debug rom, where the creators can access any Level/Item/Pixl/Character they want at any time. My reason for this is because if you look closely at the score it shows in the video when he's at Chapter 5-3, you see that the score is 00000000. I beat a file at the lowest level possible and know that it is NOT possible to have that score at that point; you need to have beaten around 4-8 bosses. What do you guys think? I think it's a little suspicious, but I don't expect this too be taken too seriously. Even if we managed to get that prototype, it's not like there would be anything different besides sounds.
By the way, for those who were wondering what the lowest level you can beat the game at is, it's 6 :).