The southern half of Route 104 connects Petalburg City with Petalburg Woods to the north and Route 105 to the south. A cottage belonging to Mr. Briney is located on the south side. This route is a good place to catch a Marill, which can learn any four of the five HM moves that will be required to finish this game. It will be very useful if you cannot or do not want to teach those HM moves to the Pokémon that you use in battle.
Deep inside the woods, you come across a researcher from Devon Corporation, a company based in Rustboro City. After explaining that he is looking for a Shroomish, he is suddenly confronted by a member of Team Aqua. The thug had planned to ambush the worker when he left the woods, but grew too impatient for that. Defeat him in battle and he flees the scene, but not before hinting that his friends are up to something in Rustboro. The grateful researcher gives you a Great Ball as thanks. He then heals your Pokémon, and rushes off to Rustboro after realizing what his attacker wanted.
The Pretty Petal Flower Shop is run by three sisters. Talk to the eldest sister teaches by the door to learn about Berries. After obtaining the Dynamo Badge, she will sell you plant decorations for your secret base. The middle sister hands out the Wailmer Pail when you first speak to her. The youngest sister will hand out one random Berry from a group of eight every day.
Stop by the Cutter's house next to the Pokémon Center. When the city was expanding, he taught his Pokémon a move to help clear the surrounding land of trees. He no longer needs his HM01 (Cut), and gives it to you. In the field, Cut may be used to clear away small trees and tall grass.
Devon Corporation is headquartered in a large stone building in the northwest part of town. The company is responsible for manufacturing many of the items Trainers rely on every day, including several variations of Poké Ball and medicine. Only authorized personnel are allowed past the first floor.
Pokémon Trainer's School
The Pokémon Trainer's School stands to the northeast of the Pokémon Center. Talk with the teacher to receive a Quick Claw, and brush up on the basics by reading the notes on the blackboard.
Just inside the entrance, you find the Man in Sunglasses again, who introduces himself as Scott. He's been searching everywhere for outstanding Trainers, specifically Pokémon battle experts. He wonders what brings you here to school, and claims that the first thing you should do as a new Trainer is teach Cut to one of your Pokémon. It's a useful field move, but using it outside of battle requires the badge from the local Gym.
It is advisable to talk to Scott every time you see him at each location that appears throughout the game as you will get a reward later.
Time for a Trade
The Rustboro Gym beckons, but before you step inside, visit the house to the east. Inside is a boy who is looking to trade his Seedot for a Ralts. Seedot is a Grass Pokémon that eventually evolves into a Grass/Dark Pokémon, Shiftry. This one is even holding a Chesto Berry to sweeten the deal.
Rustboro City Pokémon Gym
Leader: Roxanne The Rock-loving honor student!
After the battle, Roxanne awards you the Stone Badge, which boosts your Pokémon's Attack by 10% and enables the use of Cut in the field. She also gives you TM39 (Rock Tomb) as a prize.
When you leave the Gym, you witness a Team Aqua Grunt escaping from the Devon Corporation building. That same Devon researcher from earlier is close behind, and chases the thief northward. He loses track of him in the northeast, where the city connects to Route 116.
When you reach the entrance to Rusturf Tunnel, you find old Mr. Briney standing there. It seems that the thief has added kidnapping to his list of charges, as he has also made off with Mr. Briney's beloved Wingull, Peeko!
The tunnel is fairly small, so you will find the thief and his hostage shortly after you step inside. Defeat him, and he gives up the Devon Goods before fleeing. The old man rushes in to check on his Peeko, and introduces himself as Mr. Briney before the pair leaves for his cottage near Petalburg Woods.