After you get the eight gym badges, you need to train for the elite four right? What you need is a pokemon with surf, a vs. seeker, and an amulet coin is useful too. Go to One Island, go east, surf across the water, going north, past the grassy area, then you see five martial artist trainers, and a cave. Use your vs. seeker once you beat them to fight them again, and use the Ember Spa as a healing point if your guys get hurt. The pokemon you face are fighting types, levels 37, 38, and 39. This is an awesome training point before the elite four!