Dark Moon

The Dark Moon is a mysterious celestial body located in Evershade Valley. It is seen only in Luigi's Mansion: Dark Moon.  The Dark Moon has a pacifying effect on ghosts, which makes them friendly towards the living and allows Professor E. Gadd to study and work with them. However, after King Boo destroys the Dark Moon and makes the ghosts go berserk, Luigi is tasked with locating the Dark Moon pieces and putting them back together.

Each Dark Moon piece is guarded by a Possessor Ghost, each more powerful than the last due to each having the Dark Moon pieces with them longer. They are fought as follows, in this order: After collecting all the Dark Moon fragments and defeating King Boo, the Dark Moon is put back together and the ghosts return to sanity.
 * 1) The Grouchy Possessor is the boss of Gloomy Manor and possesses a giant queen spider.
 * 2) The Harsh Possessor is the boss of the Haunted Towers and possesses a flight of stairs.
 * 3) The Overset Possessor is the boss of the Old Clockworks and possesses a giant clock face.
 * 4) The Shrewd Possessor is the boss of the Secret Mine and possesses the frozen ground beneath Luigi.
 * 5) The Tough Possessor is the second boss of the Treacherous Mansion and possesses two suits of armor, three suits of armor, and then a giant suit of armor.