Pokémon Diamond and Pearl/Eterna Forest

When you enter, a woman named Cheryl will ask you to accompany her through the forest because of Team Galactic. She will not only fight alongside you in every battle, but she will also completely heal you after every fight, trainer and wild. All battles here are double battles (unless you talk to one beforehand). However, you cannot catch wild Pokemon until you have defeated its partner. Cheryl's only Pokemon is a Level 15 Chansey who knows Egg Bomb and Softboiled.