TM13, take a Sandslash named AJ. When it's a Sandshrew, it thinks that it's AJ's one from the anime, and is super tough. Hence it can take water attacks with no worries, meaning that it needs to battle every water pokemon you fight until he evolves. Also, to evolve, he needs a 100 victories, with at least 50 of them being water pokemon you encounter. As a Sandslash, the only Ground type move he can use is Fissure, since he's a boss like that.
Oh, and he needs to solo Agatha. Enjoy.
Soul Silver Pokedex: 493 seen, 493 caught
Battle Factory record: 33 wins, 29 trades.
Battle Tower record: 42 consecutive wins with 12 attacking team of: Infernape, Latios and Metagross. If only I could get at least 7 more...