The Ghost Jellyfish is a species of jellyfish that only appears in the DS version of the video game SpongeBob's Atlantis SquarePantis. It is a special specimen that appears only in the Jellyfish Shooter minigame and if the player does absolutely nothing without pausing, a Ghost Jellyfish will appear which is how they obtained their name.
The Ghost Jellyfish does not have a ghostly look. Instead, it has a poison-green color with crimson red spots and some orange streaks on it as well. It is partially transparent.
The reason why it is called a "ghost" jellyfish is that when it appears, it appears out of nowhere.