Clue 6: In Rayman 3, there are 5 of these. Clue 6a: Only 4 out of the 5 can be seen at the same time. Clue 6b: All 5 are located in secret areas. Clue 6c: Some of these cannot be obtained unless the player has achieved a certain score in a level.
There are actually 41 total Green Gems in the game (not counting bonus levels), IIRC. The full answer to the riddle is "Green Gems in the 4th section of the Tower of the Leptys", of which there is a total of 5.
I had to specify the game, but mentioning the name of the level would give it away immediately. I admit that I totally expected the first clue to throw people off, and hoped the next ones would slowly put the guesses more towards the goal, but it ended up being an all-or-nothing kind of thing.
Clue 7: This enemy was meant to appear in a canceled game, and was eventually reused in another one. Clue 7a: There is only one in the entire game. Clue 7b: It was created for Phoenix's Rayman 4.
Clue 7: This enemy was meant to appear in a canceled game, and was eventually reused in another one. Clue 7a: There is only one in the entire game. Clue 7b: It was created for Phoenix's Rayman 4. Clue 7c: It has a moustache.
Clue 7: This enemy was meant to appear in a canceled game, and was eventually reused in another one. Clue 7a: There is only one in the entire game. Clue 7b: It was created for Phoenix's Rayman 4. Clue 7c: It has a moustache. Clue 7d: It appears in Rayman Raving Rabbids for the GBA.
Well shit, I didn't expect this one to be so hard!
Clue 7: This enemy was meant to appear in a canceled game, and was eventually reused in another one. Clue 7a: There is only one in the entire game. Clue 7b: It was created for Phoenix's Rayman 4. Clue 7c: It has a moustache. Clue 7d: It appears in Rayman Raving Rabbids for the GBA. Clue 7e: It appears in the Child world.