It first appears where he haunts Castle Dedede, scaring everyone it can (but mainly focuses on King Dedede). This grim presence is actually there to scare (and eventually even gaslight) it stiff so it can pay its bills. No one knew it was one of Nightmare's monsters until the end of the episode Escargoon Squad. Escargoon first spotted this specter standing beside Dedede on a picture that he took of it standing in front of the night sky. Scared sick, Escargoon tells Dedede that the ghost must have a grudge against him. Dedede disagrees and flings the picture away. However, he soon asks Mabel to make sure he's in the clear with the spirit (Mabel of course, also predicts that the ghost has a grudge against him). The ghost appears to haunt other characters like Sir Ebrum and Lady Like as well. Near the end of the episode, Escargoon bribes Kirby, Tuff, and Fololo & Falala to dress up as ghosts and scare Dedede. When Dedede (who fainted from fear) hears him admit this he chases everyone around the castle. When the ghost monster floats towards Dedede during the chase, it thinks it's just Kirby. When it passes through Dedede though, it realizes that it was a real ghost. The ghost monster terrorizes Dedede and chases him throughout the castle (and right towards its safe) telling it to pay its bills. The ghost floats away to the monster transporter with money bags in hand.
The ghost monster is an almost fully transparent ghost with a flat, oval-shaped head and a long, wispy tail. Its head is a very pale cream color and the rest of its body is a very light gray. It speaks with an eerie tone in the original, but in the dub, its voice is very childish.
The ghost monster is also one of the few monsters that are nameless, similar to Nekketsu and Hardy.
The ghost monster is one of the few monsters that are not destroyed by the end of the episode they appear in, along with Honker Stomper.
Its expression vaguely resembles the subject of The Scream, the iconic expressionist painting.
Strangely, the ghost monster appeared in Dedede's photo and Tiff's flashback, while in Escargoon's story, the camera was sabotaged and the ghost chasing Tiff was a fake; however, that is probably because Escargoon still did not know about the ghost monster.