Things You'll Need
Instructions
Enter Sunyshore City from Route 222. You cannot get to Sunyshore City until you defeat Galactic Boss Cyrus. A man blocks the road until he is defeated. You automatically talk to Flint when you enter the city. He asks you to talk to Volkner in the lighthouse.
Talk to Volkner inside the lighthouse in the southeast corner of Sunyshore City. This causes him to go back to the gym.
Talk to Flint outside the door to the Sunyshore Gym to get him to move out of the way. He does not let you inside the gym until you talk to Volkner.
Step on the switches in the order of right red, left red, green, green, blue and right red to solve the gear puzzle blocking your way inside the Sunyshore Gym. This allows you to approach Volkner to challenge him.
Use Ground attacks from your Ground-type Pokemon to defeat his Raichu and Luxray. This does not require any significant strategy. Your Ground attacks do double damage, while his electric attacks do no damage in this match up.
Use Grass attacks from your Grass-type Pokemon to defeat his Octillery. Your attacks do double damage, while his only do half damage, resulting in another easy win. Avoid having your Ground-type Pokemon fight him because Octillery does double damage against Ground Pokemon.
Use Fighting attacks from your Fighting-type Pokemon to defeat his Ambipom. Using a Fighting-type Pokemon is optional. Ambipom is not very dangerous, so your Ground- or Grass-type Pokemon could probably defeat him without any real trouble. You receive the Beacon Badge after you defeat all four of Volkner's Pokemons.