Hey guys, thanks for inviting me to this forum, I didn't even know about it, it looks like a pretty cool place. I have a lot of versions of Rayman 1 (PC, Forever, 60 Levels, Gold, GBA, GBC) and 2 (Dreamcast, PS2, PS1, PC, GBC) I can also answer about too....
But okay, I'll tell you about the Rayman 3 Gamecube version, which is the best version since it has 3 additional minigames. It's also more complicated to unlock stuff, so this will be a long post.
I don't know how many people here also have it on Gamecube, but I can confirm a few things. Part of unlocking things in Rayman 3 on Gamecube requires a Gameboy Advance and Rayman 3 on Gameboy Advance.
The two major games on Gamecube that aren't on any other game systems are Mad Trax and Wheelis. Mad Trax requires 2 players: one who plays Rayman on the Gamecube, and one who plays the tetris part on the Gameboy Advance. So in order to play you need a gameboy advance and a link cable. It's a pretty long extensive game, and tough to win but I have beat it.
Here is an article on how Mad Trax works on Gamecube with screenshots and videos:
http://gameboy.ign.com/articles/390/390187p1.html
Wheelis is the same game as Mad Trax but is split screen, and requires you to have 4 players to play. So you need two GBAs, two link cables, and two gamecube controllers. You play on teams of 2, each team races separately to get to to the end first.
To unlock Madtrax and Wheelis all you have to do is get a maximum amount of points, just the same as unlocking in any other version of Rayman 3.
And Spiraldoor I can confirm Gamecube DOES have 2D Madness 1, or regular 2D Madness which takes place in the Jungle, it's just more complicated to unlock. I'm sure if you have the Gamecube version you have two spaces that say "unavailable" right?
Well in order to unlock 2D Madness 1, you have to have Rayman 3 on GBA, a GBA, and a link cable. From what I can tell all you have to do is connect Rayman 3 on GBA to Rayman 3 on GC in the menu screen under the minigame section where it tells you to connect to the gamecube. (I'm a little hazy on exactly what the menus say, I can check for you guys if you want.) But by simply connecting you unlock the first 2D Madness, I'm pretty sure you don't have to have 100% completion on Rayman 3 for GBA.
The next secret involves you having to beat Rayman 3 on GBA with all lums and 100% completion. If you all haven't played the GBA version yet, you should, as it's a really great game that is a 2D platformer just like the original Rayman but with Hoodlums.
Once you beat Rayman 3 on GBA, go to the Gamecube island on the map screen while it is hooked up to Rayman 3 on GC inside the connection menu. You can unlock 10 extra levels that on the GBA version. These levels are very hard and I've beaten all 10 but I didn't get anything for it except for check marks besides the levels. Each level requires a certain amount of lums to unlock.
So, that's all the secrets I know about detailed out for you. But the last secret, which is supposed to be 2D Madness 2, which I was told to come here about, is said to exist, but I can't figure out how to unlock it myself. If anyone has the Gamecube version and has unlocked everything up to this point, they will noticed under their minigames menu they still have a slot that says "unavailable." I asked Ubisoft support about this at least 5 times and they refuse to answer and tell me to go to IGN or GameFAQS. I have only seen a screenshot once on the old official Rayman forums that someone posted to their photobucket account. It took place in Picture City from Rayman 1. I should have saved the screenshot.
There was from what I remember two different forum members who were talking about 2D Madness 2 and I asked them how they unlocked it but they never got back to me. Then a few months later, the forum was hacked and erased about the time Raving Rabbids came out.
From what I understand, these are the instructions they said for unlocking 2D Madness 2:
First off, you have to have Rayman 3 for GBA, as well as a Gameboy Advance and a link cable. Then you have to have beaten Rayman 3 on GC as well as unlocked every minigame so far and beaten all of them, including Mad Trax and Wheelis. Then those 10 extra levels on Rayman 3 GBA must all have check marks by them and beaten completely with 100% and all lums. So once everything is completed, what you are supposed to do is hook up the GBA to the Gamecube with Rayman 3 and go to the menu with the GBA hookup and it should automatically unlock 2D Madness 2.
The problem is, I can't get this to work. I think I'm missing something or doing something wrong. Something that is weird is when you beat minigames on Rayman 3 for GC, it puts a red circle next to the game, as I'm sure you guys have noticed. But on both MadTrax and Wheelis, I can't get the red circle to appear when I beat them. There is a GBA symbol that appears on the other side. Is a red circle supposed to appear? I don't know...
Also one of the forum members said when you unlock 2D Madness 2 you also unlock an 11th extra level on Rayman 3 GBA at the same time. I haven't gotten this to work either
So I know this is a super long post, but maybe this answers a lot of questions a lot of you guys have and maybe you can help me figure out how to unlock 2D Madness 2.