Because if you even DREAM of using the world's greatest Pokemon, then you need to back it up with the world's greatest Trainer's moveset. Sassy? you may ask, of course. Ash knows what he's doing, and Sassy is definitely the best nature for Pikachu. "but what about Lightning Rod, don't you want immunity?" IMMUNITY IS FOR WHIMPS. Aside from that, the moves are the cream of the crop. It offers extreme type coverage, and even grants you compltely necessary priority. Note that if you input the Konami Code you can use special moves such as "Aim for the Horn" and "Electro-Iron Tail" to deal extreme damage to foes no normally beatable by the average Pikachu.