So I was playing around in the Dreamcast version of the game when I found something rather interesting, that I don't believe is currently known, and allows you to access 4 of the 6 minigames found on the Dreamcast version, including the exclusive "SPA" minigame

! Another interesting thing about this is that it gives names to these minigames, and all of these differ from what they are called elsewhere. I found this after seeing some text while looking at some of the games files in a hex editor, and experimenting in game to try to get it to appear.
You can do it by finding a waterfall in the game that you can stand behind (I have tested the two waterfalls in the Woods of Light, the waterfall in Globox Village, and the waterfall in section 3 of Whale Bay). Stand behind the waterfall and press a button 20-30 times (listed below) to gain access to the minigame:
For Lift (LIF dlc): Press the A button 20-30 times.
For Invade (SPA dlc): Press the B button 20-30 times.
For Toile (Weblums): Press the X button 20-30 times.
For Pyram (Pyralums): Press the Y button 20-30 times.
After you have done this, a message will be displayed reading "[MINIGAME] | Bonus Stage | Access Granted" and you'll be transported to the minigame.
The only problem is exiting Lift or Invade will take you to the title screen, and exiting Toile or Pyram will take you to Globox Village (you can use this to get to Globox Village before you have rescued Ly).
Sorry if this has already been discovered. I have searched Google and the forums to try and find if it is known but I haven't found any results. And in case anyone wondered, this doesn't work in Rayman 3D

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