you can go back to the CELESTIAL TOWER...where you'll meet Alder, near the ringing bell-he tells you that he wants to battle you- you'll have to return to the pokemon elite 4, who will be stronger than the first time you battled them. you could also just try FINDING pokemon to fill up your pokedex, and maybe try catching some rare ones. spend as much time as you want RAISING THE LEVELS of ALL your pokemon... make em ALL LEVEL 100!!!!! IF YOU CAN ;)