It's not hard to find, but in my opinion the best in the series. You get to play as Bowser (in addition to Peach), there's a whole Star level where Mario becomes a pro-wrestler type fighter named "Gonzalez" with lots of cleverness, you run into Luigi several times as he talks about his own hilarious "Paper Luigi" adventures, and several other great funny moments along with extra play mechanics such as "style points" in battle and even interaction with the crowd watching your battle who can help or hurt you (with you having to decide on a moment's notice if you will attack the potential crowd crasher instead... or not react and get a bonus item). Really fun, even after multiple play throughs. (And I know I'm forgetting lots more...)