I heard it differently. You go to the clearout sale after you've gotten all the Pokemon and have 999999 money. Then you buy the ticket from a lady and then go to Pacifilog town. Go to the yes no guy and say no, then no again. He gets angry and so battles you. When you beat him, your rival comes in and battles you with six level 100 Pokemon. He/she has Jirachi and Deoxys. If you win, you get to pick only one of them.
Well that's what I heard, but I guess it's not true :P
Latias_Ex