By talking to Dawn at the entrance to Kero Sewers after catching all her Pokemon, the party can engage in battle with them in a short boss rush. The following battles must be won without changing your party or refilling your inventory (although the party is fully healed between fights):
In addition to the Pokemon having more health and some having more damage and moves, every three turns Dawn will heal a random active Pokemon for 30,000 HP.
The prize for winning is 100 Galaxy Coins and Choice Ring. If the party already has Choice Ring, the prize is just 100 Galaxy Coins.