Luigi's Mansion Object Edition (Also Known as X's Mansion), is a launch title for the Object Gamecube initially released in 2008, and the first installment of the X's Mansion series. It marks the second time where X is the main character, with Four playing a supporting role, the first being Four is Missing! The game marks the debuts of King Evil Leafy, X's main antagonist, as well as Professor Seven, a major supporting character in the series.
X, having won a mansion in a contest he did not enter, arrives in Evil Woods and locates it. He enters the mansion and is soon attacked by a Object, but Professor Seven appears and attempts to vacuum the ghost with his Poltergust 3000. Though his attempt fails, he introduces himself to X before quickly escorting him to his laboratory near the mansion when more ghosts appear. In the lab, Seven tells X that the house is an illusion that has appeared out of thin air, where Mario has been captured by Evil Leafy and his minions. He gives X the Poltergust 3000 to vacuum up ghosts and the Game Boy Horror to communicate with Seven, scan objects, and see a map of the mansion.
X enters the mansion, sucking up ghosts and finding keys, while meeting Mephone 4 along the way, until he encounters a portrait ghost named Book and defeats him with the Poltergust 3000. He does the same to Mirror, and fights Baby Bottle, who sucks Luigi into his crib and fights him as a giant ghost, but is defeated and sucked into the Poltergust 3000. With his ghost-hunting vacuum filling rapidly, X returns to Seven's lab and empties it, turning Book, Mirror, and Baby Bottle back to normal.
X enters Area 2, another area through a previously blocked door and fights more Objects. After defeating Firey and Leafy, he enters the Storage Room and hits a switch, which opens a trapdoor where 50 Nickels and their leader, Evil Leafy, are hiding. All of them escape, flying into different rooms of the mansion. Luigi returns to Seven lab and Seven tells him that the Nickels were the ones who were brainwashed by evil leafy - Luigi must capture the Nickels to weaken their power, as they are stronger in greater numbers. So X goes through the many rooms of the mansion, vacuuming up any Nickels he sees. He also meets Fortune Cookie, a fortune teller ghost, who tells him to bring her any of Four's items he finds lying around in the mansion so she can get details on his whereabouts. The items are Four's Eye, Four's Value, Four's Toe, Four's Letter, and Four's Star. After sucking up Noodles, Tune, Burger, and Anchor, X enters the Cemetery and fights the shadowy ghost, Pumpkin. He defeats him and sucks him into the Poltergust, which he then empties at Seven's lab to turn all of them back to normal.
X enters a third area into the courtyard. Down the well, he sees into Evil Leafy's altar and discovers that Evil Leafy has imprisoned Four in a portrait. Four becomes desperate to save his friend as he reaches out for him. He goes through new rooms of the mansion, finding Four's items and vacuuming up nickels, including Possessed objects Ipod, Bath Bowl, Scarfy, 8 Ball, and Speaker boxes. After X brings Fortune Cookie all five of Four's items, he tells him that he sees Mephone 5 in a vision, which is shocking because Four defeated Mephone 5 and he suspects that Evil Leafy revived him. With his job done, she tells Luigi to suck him into the Poltergust so she can return peacefully back to normal. After he does so and defeats 20 Nickels, he enters the balcony and fights Spongy, a big Boi made up of fifteen individual Nickels. He throws him into a unicorn statue to split him into his individual Nickels and sucks them all into the Poltergust. He then empties the Poltergust at Seven's lab to turn all the portrait ghosts, including Spongy back to normal.
When X enters Area 4 in the attic, the mansion is suddenly struck by lightning, creating a blackout throughout the mansion. He then goes to the breaker room to turn the power back on, but finds it locked. X looks for the key and soon encounters a guy named Poop and defeats him to get the key. After he turns the power back on, he catches more nickels and portrait ghosts, including the Tranquilizer Gun, Skittle, Blood Jar, and Ice Cube, before entering the room of Paint palette, one of the most prominent portrait ghosts who is painting regular ghosts. He sends several waves of ghosts after X, but X defeats them all, causing Paint Palette to go into a state of depression and X sucks him into the Poltergust without much resistance. He then goes to the Secret Altar down a creepy hallway in the basement and encounters Evil Leafy, who reveals that he was the one who told X that he won the mansion in a contest and set it up as revenge for all the trouble Four and X had caused him. Evil Leafy goes into Four's portrait, which turns into a Mephone 5 portrait and sucks X into it. In an arena resembling the roof of the mansion with fire in the background, X fights what appears to be Mephone 5 (as Fortune Cookie's vision had seen), but when he hits him in the head with an explosive, spiked metal ball, "Mephone 5" is revealed to be a protective suit worn by Evil leafy. Luigi defeats Evil Leafy while avoiding the Mephone 5 suit's head and sucks him into the Poltergust.