When a spelunker dies in Co-op (or deathmatch, given the Ghost option is active), they will become a spelunker ghost. Spelunker ghosts can move in any direction(with a slippery traction), through walls, and can blow puffs of air with X/Square, which push items and enemies in a 2 block range, stunning them like a whip does (not dealing damage). This can be used to assist or hinder living players until they are revived.
They also visual effects. They can spin in a circle with the rope button, stretch themselves vertically with the bomb button, and pulsate a few times with the jump button .
If a camera is used on a spelunker ghost, they will freeze and perform a pose of some sort, unique to each spelunker. They are also able to make a pose while performing a spin.