Soulseeker is a great card if you use it the right way. Soulseeker gains AP and HP from each death on the battlefield, so the trick is to keep Soulseeker out of harm's way while sacrificing your 1AP/1HP pawns. When Soulseeker gets strong enough, nothing can stop him! A good strategy to use is pairing it with Sacrificial Altar and using Bonemancer to spam and sacrifice skeletons. Watch out for Engorger, though-- if your opponent plays him, odds are you'll end up fighting AGAINST your own Soulseeker!
Strong Against: Anything that can't kill it!