Cynthia has a different variety of Pokemon, unlike the Elite Four. She has strong Pokemon but not unbeatable. I suggest you have a strong fire and water type for about 4 of her Pokemon. Also, I found it easier to have a flying Pokemon with a quick claw and a Lucario with ExtremeSpeed. Just act as though she is a normal trainer and have a Max revival or a revival herb to hand.
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Celestic town
You then have to beat Cynthia
you go to the hall of fame and all the Pokemon in your party get a ribbon that proves you beat Cynthia after that there is a long credit roll
impossible
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