In my latest demo session, Nintendo laid out a big surprise -- Luigi's Mansion: Dark Moon has a full-blown multiplayer -- and it has local, download, and online play! In multiplayer, one to four different versions of Luigi climb the "scarescraper," a tower of semi-randomly generated room sets. You can choose from among scarescrapers with 5, 10, 25, or endless numbers of floors and three difficulty levels, normal, hard, and expert.
I spent some time playing Hunter Mode, which suggests there are other multiplayer types that they haven't yet revealed. In Hunter Mode, players must clear the entire floor of ghosts within a limited time. The gameplay is simple -- explore the mansion, find the ghosts, and suck them up with your vacuum. Time is relatively short, so it works best when players spread out to uncover the ghosts and then pair up to bring them down. Players generally play cooperatively, but in Zelda: Four Swords style, players also compete for coins.