Rock has to be one of the harder ones if only due to the fact it has five weaknesses that are all VERY common in the game(Fighting, Grass, Ground, Steel, Water). My limited mono rock run taught me everything has either a grass or a steel move so it was very difficult to get around some of gyms. Hardest gym was probably Shelly. Why? Wormadam. Having no fighting or fire moves ya...That thing was a little bit of hell. It IS very possible to do as I have finished the current episode and I'm excited to start it up again with the next one.