A One-Eyed Big Boo called Zycloboo wants to conquer the Mushroom Kingdom, and like Bowser in "The Second Reality Project 1" he wants to use the power source from another dimension called the Second Reality to achieve his goal: to get Mario out of sight (or maybe for some other reasons?) He warps Mario and his castle into the Second Reality. Mario's only chance to stop Zycloboo is to find the Power Supply station, which can give him the power he needs for the task - or at least that's what Zycloboo told him, heeheehee!
Note: This hack isn't working right in ZSNES v1.42. Older versions (like v1.36) and newer versions (like v1.50) will work.