I remember encountering some glitches myself...
I'll start from the most recent one...
1. Rayman 3: Hoodlum Havoc;
I think that was the last part of The Longest Shortcut...
The very beginning of Summit Beyond the Clouds(sp?).
This strange layer appears randomly at the beginning of the level and lasts for the remaining of the gameplay...
Solution: Sometimes quiting the game and entering it works (by quiting I mean playing other minigames/doing whatever else that doesn't have anything in common with the level and causes quiting the game from that savestate).
(during the gameplay it also happened to me in Razoff's mansion, the underwater level and in Hoodlum's HQ [twice] - that's how I can assume there's no real pattern of when that may occur)
2. Rayman M;
[no picture]
Only my niece can perform that glitch - I can't...
I think it happens in the Nebula Tower - the final part of the lap (with those skeleton things).
If you get hit by any of the skeleton tails while climbing up the next platform at the right moment, your character might end up "floating" (the character freezes in the falling animation). You can move around with the character in such state but only on that platform. After:
- falling down;
- getting hit by that thing again;
- pressing the jump button several times; the character goes back to normal. (I don't remember if hitting the optimalisation button would do anything)
3. Either "Amazing learning with Rayman" or "Maths and English with Rayman" (don't remember which one but I think it can happen in both);
[no picture again - sorry]
You may know or not that Rayman can't learn how to run in these games - he can do that in the last level because of Mr. Dark casting a spell in certain point of said level, though. Once the spell ends, he's unable to run again...
If I remember correctly, when you hit the action button while the spell ends, you might be able to make Rayman run anytime you want with said button.
Rayman won't be able to perform the grimace thing during the glitch/bug and it ends with the end of the level...