I can only answer with Infernape as the Starter, and have no idea of how to use the other two. Also, I use Pearl.
So, i start off with my level 87 Infernape out the front, use Blast Burn once. Spiritomb is dead. Cynthia will then change to Gastrodon, I bring out level 55 Roserade, Petal Dance. Dead. She will then bring out Garchomp and, because I use Pearl, I bring out level 78 Palkia and use Blizzard. Now, unless you've traded with someone to get yourself a Palkia, you can just use another high level Pokemon that has Ice or Dragon type moves (Dialga may be good, I'm not sure). After Garchomp Cynthia will bring out her Milotic. Probably one of the toughest Pokemon of any Champion as she has a full restore for it and it uses Aqua Ring, which restores a little bit of HP every turn. You can quite easily negate this with a Giratina at level 80 by using the move Heal Block, and then using Shadow Force to knock it out. Then she will bring out her Roserade. Switch back to Infernape. Use any fire type move it has. She will lastly bring out her Lucario, and you will keep your infernape in battle and use another fire type move.
You have now completed the league.
She will if you have beat the elite four and the champion.
The Pokemon Champion is Cynthia
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beat the elite four and the champion
Yes, you can get Azelf back if it faints during your challenge against it but it will only come back in Pokémon Platinum, Pokémon Black 2 and Pokémon White 2, it will come back once you beat the Champion regardless of whether you've already beaten the Champion or not. However if you've knocked out Azelf in Pokémon Diamond or Pearl then it will not come back.
Beat the Champion Cynthia
you go there after you beat the champion on diamond.
beat the elite four and shes the champion
She will if you have beat the elite four and the champion.
you wake up in your house again
You eventually have to beat her. She is the champion to the elite 4. So after you beat them you beat her, become a champion, and your Pokemon go into the hall of fame. So choose your favorite Pokemon!
you do not see her any more you only will see her at celestic town after you beat crasher wake the 4th gym leader
Beat all the elite four and there champion
you need to have a wide variety of types and at a level of at least 60
Beat the Champion, talk to the boatman in Snowpoint City.
You have to get all 7 Gym Badges, beat the Elite 4, and defeat the Champion, Cynthia.
u must first complete your pokedex and beat the champion