Alright. I went to bulbapedia but this is all I got.
"When one finishes the Stark Mountain quest, instead of the rival appearing at the Fight Area on weekends, he now appears at the Survival Area in front of the Battleground. During the first battle, the levels of the Pokémon in his party range from 59-65, second battle 69-75, and third and beyond 79-85. On his last battle, he is the trainer with the highest-leveled Pokémon in all main series games."
Here's the page link if you need it.