Cynthia is not the champion in the johto region in Pokemon heartgold,you can't find her in it, but she is the champion in Pokemon pearl,diamond, and platinum versin and that is the sinnoh region.
Cynthia is the Pokemon League Champion, and she appears after you defeat the Elite League (The first 4 people). You have to defeat her to become the champion.
Champion Cynthia has a level 66 Garchomp. It's pretty strong, but a guy with Ice Beam will probably be able to handle it. I beat it with rock tomb, on a level 53 Geodude, its weak
The champion is Pokemon Diamond, Pearl and Platinum, is Cynthia. She has various Pokemon-types. She is the Sinnoh Champion. Her Pokemon are Spiritomb, Lucario, Togekiss, Milotic, Garchomp and Roserade. In Platinum, Cynthia has a Togekiss. In Diamond and Pearl, she has a Gastrodon.
Cynthia is a character in the popular nintendo video game pokemon. During the game she will give you a charm that you need. She will do so after you complete beating the pokemon league.
You find Cynthia in a villa in Undella Town across from the Pokemon Center. For the first time battling her,she asks you your name. Later, she'll appear in Spring/Summer for DAILY battles. Her Pokemon are at the same level.