Polterpup

Polterpup (also known as ???) is a specific Polterpup character who appears throughout Luigi's Mansion: Dark Moon. Unlike normal Polterpups, he has a red collar instead of blue. He is also the only ghost with no actual name. E. Gadd surmises that Polterpup is lonely and is looking for someone to play with, but its attempts to do so accidentally cause trouble for Luigi.

History
He first appears in Gloomy Manor, where he is playing in the Mudroom Exterior. He finds a jewel underground and plays with it shortly before getting it stuck in a tree. At this point he leaves the Manor.

Later, he appears in Haunted Towers after Luigi finds the key in the pool, he runs up and takes it. He plays with it, similarly to what he did with the jewel, and throws it out the window. He chases after it, and is not seen until the next level, where Luigi hunts him down. Luigi finally catches him, but before he can store him in the Ghost Container, the pup managed to escape from the Poltergust 5000 and flees yet again.

He returns in the Old Clockworks, where he steals the second Clock Hand from a group of Greenies. Luigi has to chase after him yet again before finally catching him in the Poltergust 5000; unfortunately, the pup still manages to escape before he can be stored away.

He returns again in the Treacherous Mansion. Just before Luigi can go through the front door, Polterpup jumps out of the keyhole and knocks the key out of Luigi's hand. He flees to the basement, causing a long and paranormal chase through the odd rooms. This time, E. Gadd manages to have fixed the Ghost Container, meaning that the Polterpup can't escape.

He is finally released from the container in the end, after turning normal. Unfortunately, without anyone to play with, the pup isn't quite as happy as everyone else. But Luigi cheers him up, and after taking a picture with the other ghosts, Mario, and the Toad Assistants, he returns home with the green-capped hero.

Also, whenever Luigi loses all of his lives, if he has a Gold Bone with him, Polterpup will come up to him and lick him to health, even if the dog's trapped within the Ghost Container.

In-Game Description
??? - ''I haven't come up with a name for this mischievous and adorable Polterpup yet. He's caused us a whole mess of trouble, but I think the playful tyke just wants someone to take him in.''