Instructions
Obtain the Stone Badge, Knuckle Badge, Dynamo Badge and Heat Badge. Norman will refuse to battle you unless you possess all four.
Travel to Petalburg City. The city is west of Oldale Town.
Enter the Petalburg Gym in the north section of the city.
Defeat the Cool Trainers throughout the building. Each of these trainers has a Level 27 Pokemon and specializes in a different aspect of battle. For example, one of the trainers focuses on defense, while another focuses on one-hit knock out attacks. The Gym specializes in Normal-type Pokemon, so use Fighting-type attacks to seize the elemental advantage.
Defeat Norman's trio of Normal-type Pokemon. He has a Level 28 Slaking, Level 30 Vigoroth and a Level 31 Slaking. The Slaking have the Truant ability, meaning they can only attack you every other turn; however, when they do attack, they can cause great damage. Use a Ghost-type Pokemon, such as Haunter, to battle the second Slaking, whose Façade and Focus Punch attacks cannot damage Pokemon of that type. The first Slaking can use Faint Attack to knock out a Ghost easily.
Receive the Balance Badge and TM42 (Façade) for your victory. Norman will also tell you to visit Wally's house.
Leave the Petalburg Gym and visit the house next door.
Talk to Wally's father. He will give you HM03.