Super Mario World: Bowser's Cataclysmic Trap is an aesthetically vanilla hack in that most of its graphics are based on those of the original game. In this hack, Bowser has kidnapped Luigi to set a cataclysmic trap for Mario. Why Luigi? The real world answer is that 2-player mode caused glitches involving the overworld music. They weren't game-breaking and seemed to only consist of the wrong track being loaded when going to submaps with Luigi. Oh well. At least it's not Peach.