Luigi

Luigi, having won a mansion in a contest he didn't even enter, enters the Boo Woods and locates it. He enters the mansion and is soon attacked by ghosts, but Professor E. Gadd appears and fights off the ghosts with a vacuum. He tells Luigi that the mansion appeared out of thin air and is an illusion, and that Mario was captured by the ghosts living within the mansion. He trains Luigi to use his vacuum invention, the Poltergust 3000, to vacuum up ghosts, and that he had several ghosts captured and turned into portraits, but they were released by King Boo.

He encounters King Boo, who reveals that he was the one who told Luigi that he won the mansion in a contest, and set it up as revenge for all the trouble they caused him (though they may not have met him before, they have been fighting against Boos for years, plus King Boo works for Bowser). King Boo goes into Mario's portrait (which turns into a Bowser portrait) and sucks Luigi into it. In an arena resembling the roof of the mansion (and with a slight resemblance to the arena at the end of Super Mario 64), Luigi fights Bowser (as Madame Clairvoya had seen), but when he hits him in the head with a bomb, it is revealed to be King Boo piloting a giant Bowser suit. Luigi defeats King Boo and sucks him into the Poltergust.

Luigi returns to the lab and turns all the portrait ghosts, including King Boo, into portraits again. E. Gadd then reverses the Portrificationizer to release Mario from his portrait. After Mario goes through a reverse-procedure of all the portrait-ghosts captured, he rockets out of the machine, colliding with Luigi, but being otherwise alright. Luigi laughs and cries with happiness that his brother is safe. Since King Boo has been defeated his illusion of a mansion fades away, though the money and jewels Luigi collected in the mansion was real, and with it he gets a new mansion or house. But if Luigi gets H rank, he ends up with only a tent.