Luigi is walking to his new mansion with shaky boots; he seems to have won it via a contest he didn't enter. A quick run-in with ghosts and an explanation from Professor E. Gadd makes things clear: the ghosts have tricked Luigi. E. Gadd also tells Luigi that he saw Mario walk into the mansion, but dismissed him on the assumption he was an illusion. Knowing his own brother is in danger, Luigi learns the basics of ghost catching from E. Gadd and heads inside the mansion.
Luigi progressively gains more and more access to the mansion and recaptures all of the ghosts E. Gadd had previously caught inside paintings. This finally catches him up with King Boo, who's quite angry Luigi caught all of his friends. King Boo fights Luigi using an illusory body of Bowser, but Luigi captures him and is returned with Mario, who's trapped in a painting. Thankfully, E. Gadd's Ghost Portrificationizer works in reverse, and that's able to return Mario to his round self.
- Mario & Luigi meet Professor E. Gadd for the first time.
- Luigi’s NEW Mansion is built.
- King Boo is captured within a painting.
- King Boo wants revenge on Mario & Luigi for something, that potentially being what occurred in Super Mario 64 DS.
- Vincent Van Gore’s painted ghosts and Luigi’s Mansion appear here for the first time.
- Neville reads a book titled “Mario Story”, which is the Japanese name of Paper Mario. Herringway was stated to be writing a book by that name in the ending of Paper Mario, likely placing this game after that title.