Dear ellzierocks,
It is completely different...Like Matt explained, 5 mansions, funner bosses, and all that. Here are some differences, 1. The bosses: There is 1/2 boss battles per mansion, but in the last mansion, there are 3. 2. Different Ending, Different Beginning: In the beginning, E. Gadd is researching Ghosts and is being helped by Greenies, then King Boo destroys the Dark Moon with his power. E.Gadd then flees from the Gloomy Manor (1st mansion) and goes to his lab to call Luigi, who is in his poor mansion...(yes it is his mansion)In the end, you fight King Boo, no Bowser costume, He has 3 phases, 1. Battle 2. Run from King Boo and 3. Battle again. Also at the end BEFORE the battle, King Boo wants all of the Dark Moon pieces from Luigi for Mario, which is again trapped in a portrait.Happy to help you
Sincerely,
LuigisMansionDarkMoon
3DS Friend Code:1246-8984-3513