A Waterwraith.
Waterwraith
Amphibio sapiens
A Waterwraith is what is believed to be a liquid or ectoplasmic creature. It is said that it may even be created from the fear of other things. It is found only in the Submerged Castle (all sublevels), and in the Bully Den in Challenge Mode. It appears to have a human shape, a head, body, arms, and legs, without distinct characteristics though since it is transparent and it is quite heavy. It falls from the sky and moves around on these "rollers". It will chase you and your Pikmin, but is more directed on the active captain. It is invincible to any Pikmin assault, even if petrified, EXCEPT when attacked by Purple Pikmin. However, it strangely can't be hurt by purples if petrified, unless they are thrown in a perfect arch so they make the sound they usually make when they land. When a purple lands on or near the Waterwraith, it turns dark, and becomes vulnerable to ALL pikmin attacks, but it is not wise to do this when it is on the rollers. When you deplete its health, the rollers crumble and the Waterwraith will run all around the cave. Hit it with more purples and then you can easily attack it with other Pikmin. When you finish it, it will vanish into nothingness and you will be troubled no more. It drops the Professional Noisemaker the first time you beat it in the Submerged Castle. It is perhaps more ghost like because in go through others that are already solid. This may also be a minor glitch.
NOTE: In the Submerged Castle, you will only be able to get purples on the last sublevel (5) via the Violet Candypop Buds.
In the Bully Den, you will already have 25 purples, but no other color of Pikmin. There are also 2 Waterwraiths in there.
It is also one of the few enimies to have "different music" (Along with the Giant Breadbug and Titan Dweevil). In Sublevels 1-4, when it appears, a "scarier" version of boss music plays. When it has no rollers, a more "entertaining" music plays.
It may be fat too. Because with no rollers, it's sides seem to "jiggle".
Olimar's Notes
All that is known about this creature stems from a few sightings deep underground. All reported sightings feature the same core sets of details: a giant, vicious form with a clear, hazy sheen not unlike hard candy. One theory holds that it may be the ectoplasmic incarnation of a kind of physic phenomenon, but as is usually the case with such theories, it is very difficult to prove. All witnesses report being suddenly overcome with fear upon sighting the creature, approaching a state of panic and near insanity. In fact, every report an inordinate amount of extremely vague details, which has led to suspicion that exhaustion and fear have caused some simple natural phenomenon to be viewed as a living creature.
Louie's Notes
Inedible. Known to cause mass hysteria, followed by leg spasms and internal thunderings. Cat Shit