In Rayman and its spin-offs
In the original Rayman game, they are found in all worlds, except for the Dream Forest. There are many kinds of clouds. Some of them are static, and others follow various trajectories. Among static clouds, there are rebounding and trampoline clouds, the latter allowing Rayman to jump higher with the correct timing. The are also also vanishing clouds, which disappear once Rayman steps on them, or at regular intervals. During the battle against Mr Stone, moving vanishing clouds appear, but these occur nowhere else.
In the Atari Jaguar version of the original Rayman, vanishing clouds have eyes, which snap open to reveal a malevolent face an instant before they disappear from under Rayman's feet. These eyed clouds, however, do not open their eyes in any other version of the game, but they do still appear to have closed eyes.
In Rayman 3
In the Nintendo DS version of Rayman Raving Rabbids, clouds appear in several stages. They start out transparent and not solid, though can be made solid by using the wind costume. They act as platforms used to get across large gaps. They will however only remain solid a set amount of time.