Lavaridge Town gym is a Fire type gym, so you want Water, Ground and Rock type Pokémon.
Slugma (Lvl. 26) – Fire
Numel (Lvl. 26) – Fire / Ground
Torkoal (Lvl. 28) – Fire
Use a water Pokémon to take out Numel, as the moves will be 4x effective. The entire team tries to use Sunny Day throughout the battle, which will weaken Water type moves whilst strengthening Fire type moves, so you want to take out the Pokémon quickly so that they do not use it. Use Water, Rock or Ground moves to take out Slugma and Torkoal.
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