i have been researching that myself!i've heard you finish the game,i've heard you can't rematch.i don't know what to believe,but you could try that,or go on Yahoo!answers.com or seribiinet.com.hope this helped!
On Pokemon Black and White, Clay has Krokorok level 29, Palpitoad level 29 and Excadrill level 31.
Outside the Chargestone Cave.
defeat team plasma at twist mountain
you need water types or flying types and they are high level
After you beat Clay in Pokemon Black and White,he said that you have to go to Route 6 and into Chargestone Cave.
walk in to the city where his gym is and then you will have to go to the ice box andthen battle his gym
As you head out of Driftveil city after you defeat Clay, you will run into Bianca. Battle her and she will give you Fly
Driftveil City
My guess is about 40.
its clay as a gym
you go to the cave that has the yellow wed in front of it and clay will destroy it for you to pass
On Pokemon Black and White, Clay has Krokorok level 29, Palpitoad level 29 and Excadrill level 31.
Outside the Chargestone Cave.
You go to the cave that has the spiderweb on it and Clay comes along and blasts it with his Krokorock and you can go in but heal your pokemon first the cave is invested with team plasma
first you go to the cold storage ( south of drifvile city) and battle team plasma then clay will be at the gym in the north east
beat clay and he will destroy it
defeat team plasma at twist mountain