Boolossus

Boolossus, the Jumbo Ghost, is an enormous Boo and one of the portrait ghosts in the game Luigi's Mansion. This ghost is actually composed of fifteen regular Boos who can combine to create Boolossus. Although these Boos are normally timid and shy, when they form into Boolossus, all their fears disappear. The Boo is a servant of King Boo, leader of the Boos, and is the guardian of the third area of Luigi's Mansion. Unlike other Boos, Boolossus has glowing yellow eyes.

Before the events of Luigi's Mansion, Boolossus is captured by Professor E. Gadd during the professor's travels around the world. E. Gadd uses his Portrificationizer to transform Boolossus into a painting and places the painting in his gallery of other portrait ghosts. Unfortunately, the capture of Boolossus greatly angers King Boo. As such, King Boo leads his Boo minions in an assault on Professor E. Gadd's laboratory. The Boos reverses the setting on E. Gadd's Portrificationizer and reverts Boolossus's state. King Boo then orders that all the other portrait ghosts that Professor E. Gadd caught should be freed as well. Eventually, after all the portrait ghosts are released, King Boo creates a mansion, right next to E. Gadd's laboratory in Boo Woods. In Luigi's Mansion, Boolossus, along with the other Boos (including King Boo), rests in a secret area under the Storage Room. When Luigi activates a hidden door in the Storage Room, the Boos spring out. However, when they notice E. Gadd's Poltergust 3000, a ghost-catching vacuum device, on Luigi's back, the Boos decide to run off and hide in the mansion.

Eventually, as Luigi progresses through the mansion, Boolossus attempts to capture Luigi on the Balcony on the third floor. While Luigi is there, the Boo Radar on the Game Boy Horror starts flashing intensely, indicating a powerful Boo presence. Soon, the fifteen Boos that make up Boolossus appear before Luigi, circling and taunting him. After taunting him, they merge into Boolossus and whisk Luigi away to the balcony arena, starting the battle.

During the battle, Boolossus attempts to slam into Luigi. To defeat Boolossus, Luigi must use his Poltergust 3000 to pull Boolossus into one of the two placed unicorn ice sculptures located on the balcony. When Boolossus touches the sharp horn of the statue, he pops and separates into the fifteen normal Boos. Luigi may then absorb an Ice Elemental Ghost from the ice sculpture and spray frost at the Boos, freezing them and enabling him to suck them up into his Poltergust 3000. Eventually, Boolossus reforms with a lower number of Boos. He becomes faster every time several of the Boos are sucked up. However, if Luigi keeps popping him and freezing the small Boos, he can slowly drain Boolossus's power. As more and more Boos are caught, the other Boos become more wary of the Poltergust's ice blasts and flee when the ice blasts get too close to them.

After capturing Boolossus, Luigi acquires the key to the West Wing of the mansion. Defeating the boss counts as capturing a total of fifteen of the fifty released Boos. After the battle, Luigi visits Professor E. Gadd's lab, in which he turns Boolossus into a portrait.

Trivia

 * Boolossus makes an appearance in the Luigi's Mansion battle course of Mario Kart: Double Dash!! and in the race course Luigi's Mansion in Mario Kart DS as a painting on the wall.
 * Boolossus appears in the Mario UNO cards on the "Draw 4" card.
 * The name "Boolossus" is the pun on the words "Boo" and "colossus" and literally translates to "Giant Boo".
 * In the PAL Hidden Mansion, Luigi rides the Poltergust like a car during the Boolossus battle. This provides faster transportation, but also less traction.
 * Boolossus is the only Portrait Ghost to not have HP.
 * Along with King Boo, Boolossus is one of the two only Boos that are Portrait Ghosts.
 * Oddly, Boolossus is Ghost #22 in the gallery even though he is the 16th ghost caught.