You Tackle Pikachu. He Thundershocks your Onix. Thundershock wasn't so good, because Electric against Rock means Rock is probaly going to win. Now you use Rock Slide. Pikachu is getting weaker. Pikachu uses Thunder.(not Thundershock! Thunder is an attack!) You should make another choice. Should you Use Potion ? Or should you keep on Keep on attacking ? It is your decision.