Very early into the development of Rayman 2, it was a 2-D game for the PlayStation. This was later scrapped for the 3D game that Rayman 2 became. Pictures of the 2D version and concept art (a green villain with a chainsaw) and mentions of powers such as the platform fist were published in gaming magazines such as EGM. – [info from Wikipedia]
Update: It seems that a playable demo of this 2D prototype can be unlocked as a bonus level in the Playstation 2 version of Rayman 2.
Thanks to Fast Ash and Adamis Fox for the contribution!