Pokémon:
- Tangela (Level 23): Grass
- Weepinbell (Level 23): Grass/Poison
- Gloom (Level 28): Grass/Poison
Weaknesses:
Grass-type Pokémon are weak to Fire, Ice, Flying, Bug, and Poison moves. Grass/Poison types are 4x weak to Flying and 2x weak to Fire, Ice, Psychic, and Bug.
Strategy:
Fire-type Pokémon are excellent here. If you evolved an Eevee into Flareon, it will dominate. Alternatively, a Growlithe/Arcanine (found on Route 7/8) or a Vulpix/Ninetales (found on Route 7/8) with Fire-type moves will be very effective. Flying-type Pokémon like Pidgeotto/Pidgeot or Fearow are also strong, especially against Weepinbell and Gloom due to their 4x weakness to Flying.
Be wary of Erika's Pokémon using status moves like 'Sleep Powder' or 'Stun Spore'. Carry Full Heals or Awakening/Paralyze Heal. Focus on hitting their weaknesses and you should win the Rainbow Badge.
Reward:
Rainbow Badge, TM21 (Mega Drain)