Coming from the official website...
With so many new places to explore, all new ways to capture ghosts, and a brand new local multiplayer mode, Luigi's Mansion: Dark Moon is another star turn for Mario's heroic brother—and it's only on Nintendo 3DS.
This is the first we've heard of any multiplayer in the game. No idea what this mode will have us doing, but I'm excited to find out! Thanks to all that sent this in.