BW Serperior has terrible move pool for a physical attacker. Gets better in BW2 with access to Aqua Tail and Outrage move tutors, but on BW it has Leaf Blade and not much else. Could benefit from Coil, but still awful move pool.
Special move pool also lame, especially without Contrary. Calm Mind + Giga Drain could make it a great tank though. And if you get lucky, Hidden Power could provide some decent coverage.
Honestly, I'd make it defensive, with a nature that lowers whichever Attack stat you care less about and boosts either Defense or Speed. Its offensive stats are the lowest to begin with so they would get the smaller nature boost/penalty anyway.