Route 104 (3)

On your way back to Mr. Briney's hut, make sure to harvest the planted berries along the way and plant some of them again. After crossing the wooden walkway in the middle of the pool of water south of Rustboro, there lies a thorny tree that blocks the path leading to an item. Cut it down and grab the Revive in the dead end.

After reaching Petalburg Woods, you'll find another thorny tree. Cut it down and proceed to the right. You'll find a little girl there. Talk to her to receive a Miracle Seed. The Moss Rock is located in the corner of the area to the right. This is needed to evolve Eevee into a Leafeon. Grab the Great Ball near the rock then proceed further to the south, deviating from the main path.

Follow the path to the south then turn left. You'll find an X Attack. Go to the south again and then turn to the left to reach the exit of the forest. Head to Mr. Briney's house and choose to set on Dewford.