The Mystery Event!
After you beat the Elite Four, go to Petalburg City and talk to the man beside the computer. He will ask you for a profile. Tell him "Mystery Event Is Excited". After you're done talking to him, save your game and turn your Gameboy off and then back on. Then you will have the Mystery Event option unlocked on the Title screen of your Pokemon Ruby Version!
More tricks, tips and cheats for this game are right here - Pokemon Ruby cheats
Comments for this cheat