Forum:Pewter Gym (Challenge Level)

Strategy
To beat this challenge, you will need to put both Metapod and Kakuna on both sides of a lane and set them to use String Shot. Drop every other Pokémon with all their damaging moves and set Charmander to use Ember. After this wait until an Onix grabs the Pokéball and immediately change all the Pokémon to that lane and focus it down. The rest should just be taking down each Onix as they come to take the Poké Ball. With the Kakuna and Metapod slowing the Onix, the rest of your Pokémon should destroy them.

Or

Set Pidgey on Sand-Attack to make Onix drop the Pokéball, reduce Onix's Defense and Speed with Kakuna/Metapod and Rattata. Use Charmander as your main force of attack. Recommended:
 * Charmander: Ember
 * Kakuna and Metapod: String Shot
 * Pidgey: Sand Attack and Tackle
 * Rattata: Quick Attack