This glitch only works on Japanese versions and allows you to enter the "empty" Mystery Zone that fills the voids in the game's geography, allowing you to obtain the Nintendo Event-only legendary Pokemon Darkrai and Shaymin. (The promotions for these Pokemon have passed, so this glitch is required to get them without trading.) You will need access to the Elite Four and Pokemon with Surf and Fly or Teleport. In Aaron's room, face the southern door and use Surf to go through the door. When done, you will go through, now easily able to move around to New Moon Island and the Flower Paradise in the game where you can find and capture Darkrai and Shaymin as you would any Pokemon. Once done, you need to Fly/Teleport elsewhere because you cannot able to leave after that, since the events were not properly triggered. But, otherwise, the Pokemon will function as normal; the only thing to note is that obtaining the Event items for these Pokemon later will not regenerate them, and failing when using the glitch is the same as failing as normal: you only get one shot.