This is the 3rd game in the Mario and Luigi series. It has a new plot. Apparently, the citizens of the mushroom kingdom have caught a new disease that makes them swell up to the size of a car. In addition to that, Bowser seems to swallow Mario and Luigi at one point in time. You can play as Bowser in the real world and the Mario Bros INSIDE Bowser's innards. There are also rumors that Fawful has returned as a villain. Those are just rumors though, arisen from people's noticing that the enemies look like him and some people swear to seeing him flying around in the Nintendo Conference teaser video. These are unfounded though.
This game is due out February 11, 2009 in Japan. I think it's fair to assume that a US release should come out no later than the end of spring 09.
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