In Rayman 2
In Rayman 2, they are found in the Cave of Bad Dreams, and there they are used as platforms to cross the many bottomless pits. When Rayman approaches Jano, the Guardian emits skulls from his bony hands, which Rayman will have to shoot to stop them floating away, helping him cross the chasm.
Some skulls fall from the ceiling and quickly sink into the liquid below if Rayman does not climb on them quickly. Also, skeletal hands that appear from holes in the walls can sometimes carry skulls, moving them between the platform Rayman is standing on and his destination. The Elixir of Life is contained in a skull. If two skulls come to contact with each other, they will fall.
Skulls also appear in the Nintendo DS version of Rayman Raving Rabbids where they usually move up or down on a set path.