Okay Endquote, catch a Pikachu in Viridian Forest and call it Mouse. He thinks he's some kind of supermouse, so start out by soloing Misty with him. Unfortunately, the battle opens its eyes and it becomes as timid as any other mouse - in fact, it refuses to battle at all unless you have no other options (ie everything else has fainted). To make up for that, it wants to help you as much as possible in other ways - give it Flash, Strength, Rock Smash, Dig and/or any other moves that are useful outside of battle! (Ideally you can get a Flying/Surfing Pikachu instead).