Timid Nature, Max Speed and Special Attack. Focus Sash.
Use Toxic, then Protect. Super Fang, and Protect again. Then Thunderbolt, and it's all over. Best when paired with Mean Look passing, or else bring him in at the end to finish off the team. I've beaten Bronzong, Electivire, Slowbro, and Salamence by using the little squirrel. And it's so much better than doing the same with a Garchomp. XD
Anyways, yes, I like it. Pachirisu is awesome! He's actually one of my highest leveled Pokemon in Diamond, and I've used him in several winning OU battles. =D