Instructions
Defeat the Elite Four to unlock Route 40, and then head down Route 40 to find the Battle Frontier.
Enter one of the four buildings here, the Battle Tower, Battle Castle, Battle Arcade or Battle Hall. Choose six "rental" Pokemon in this area, restricted to level 50 to meet the challenge of random singles or doubles fights. Wins are tallied in sets of games of seven, and all seven games must be won to win a set. Pay attention to the perks and handicaps in each setting. For example, in the Arcade setting, random bonuses are awarded to your team and the enemy team by rolling a roulette wheel.
Win three sets of seven fights in any of these settings and a Frontier Brain will challenge you to a fight. Defeat it to continue the streak to seven sets of seven fights. The Frontier Brain will return for a much harder fight. When the Frontier Brain is beaten for the first time, it drops the Silver Medal. On defeat in the second fight, it drops the Colored Medal.