Okay, for the people who are wondering, the only rule for you to be able to compete in the Battle Frontier, is that you've beaten -at least- the Elite Four of Hoenn, the champion doesn't matter, just beat the Elite Four, and you can compete.
However, when you do apply to participate, you will have to wait for approval.
Also, in order to win at the Battle Frontier, and master it, you will have to beat everyone, but the first six have to come before Brandon. And Brandon before Votun.
