The opening of Luigi's Mansion Dark Moon is that Professor E. Gadd is studying the ghosts of the Gusty Manor, as the ghost appear helping E. Gadd with his research. Meanwhile, King Boo is outside and uses his crown to hit the dark moon and the dark moon peices go flying. The ghosts then go crazy and start messing everything up. Then the cutscene shows Luigi in his house sleeping. E. Gadd then calls Luigi from E. Gadd's room. Luigi then gets sucked up by the pixelator.
The gameplay to LMDM is pretty much the originals.
1.You do not control Luigi while you are sucking up something.
2.There are now peekholes in some rooms. You tilt the 3DS to look through. Peekholes are holes that you look through to see through to the next room.
3.There are more puzzles in LMDM than in LM.
4.You can rescue Toads that help you through puzzles.
5. The final boss is puzzle based.
Multiplayer is now implimented! But probrably not how you think. The multiplayer is OK in my opp., as everyone plays as a different color Luigi, which is sort of obscure. There are a few different modes. One mode acts as a battle mode in which you compete to suck up the most ghosts. Another is when you work together to get through the ghostly tower to the top,(this mode is kinda hard so I reccomend playing with 4 players).