If you want to challenge Cynthia, she can be challenged in Undella Town during the spring or summer. Her pokemon are as follows
- Spiritomb Level.76 (No weaknesses unless you use Odor Sleuth)
- Milotic Level.76 (Weak to Grass and Electric)
- Togekiss Level 76 (Weak to Electric and Ice)
- Lucario Level 76 (Weak to Ground and Fire)
- Glaceon Level 76 (Weak to Steel, Rock, Fight, and Fire)
However Glaceon does not have countermeasures against Fire types
- Garchomp Level 76 (Weak to Ice and Dragon, however Ice plus STAB would do 5.5X damage)
You would receive 15600 PokeDollars after defeating her. In challenge mode all of her Pokemon would be level 80 except her Garchomp would be level 82 with a 16400 PokeDollar reward. Any experience from Pokemon Platinum will be important for this one since she uses the same Pokemon as before except with higher levels.