Details: After defeating the Pokemon League for the first Time, you can Battle it again as much as you'd like afterwards. The Elite Four Members will remain the same, but their Pokemon Teams will be different and at much higher leveling. After defeating the Elite Four Members, you will be challenged by one of ten different trainers. You are the Champion after all, and many different trainers will be looking to defeat you (as your mother alludes to after finishing the main storyline of the game).