I'll give you a hint if you want: Erika and her trainers at the Celadon Gym all use grass and poison pokemon. To defeat them easily, use fire, psychic, fighting, ice, or flying typed attacks. I know, I'l give you a HM 2, which teaches Fly. Fly is a very good flying typed attack. If you use it outside of battle, you can fly to any city you want. You can only use Fly once a day though. E-mail me with the code 85330 and I'll give it to you.