Okay, I'm getting tons of SmashBoards lag, so I'll just make a quick post.
I managed to extract the entire filesystem from Return to Dream Land, so I can see pretty much everything in the game. Right now, I'm checking out all of the different file types, and I noticed that Kirby's Return to Dream Land uses the same file format as Smash Bros. Brawl does for it's music - .brstm! This basically means all the tools I need to change out the songs in RtDL are already made, so I'll be switching out a bunch of music to see how it works, and also for fun. Right now, I'm looping out the RtDL 8-BIT Main Theme to add in to replace the current one.
Also, I noticed some funny things. First of all, they made a typo, not that it matters much, calling Stone Kirby's ability "StoneKriby", while others are named regularly, such as "SwordKirby", and "BeamKirby". Also, there's a few songs in the game that have perculiar music - mainly "halberd.brstm" which is, if I am correct, the boss battle music for Magolor. There's also things such as "dedede01.brstm" which is DeDeDe's theme, "dedede02.brstm" which is a remix of his theme, and "dededesxd.brstm" which is Masked DeDeDe's theme. Also, I found this quite funny - the music used for Kirby's theme when he's defeated it called "KbyDEAD.brstm". Not sure why there's so much emphasis on the fact that he's defeated, lol.
Also, okay, I need to say this - I also found a bunch of themes from Kirby Super Star, although they were new arrangements. I'm sure these are used in the game somewhere, but I don't remember them. Some of these include Kawasaki's theme used in Gourmet Race's cutscene, "Loby.brstm" which is used in one of the menu themes for one of the sub-games in Super Star, and "st_umi.brstm" which I remember hearing in Super Star somewhere, and in Return to Dream Land. It's a fantastic theme, not sure where it's exactly from, though. To be honest, I've been looking for this for around a month on YouTube, but I could never find it. I sorta feel like this game was meant to be a Super Star sequel or something - maybe these are from when it was being developed for the GameCube? I'm sure that Helpers were in those screenshots.
I'll report more findings as I go!