I don't entirely understand why the notion of using Serperior as a early game supporter and also a lategame cleaner is considered so nonviable. I almost never regret having leech seed on a set, and I remember playing BW Dream World obsessively a couple years ago. Sub-seed Serperior was a monster, and glare with leech seed seems like an idyllic way to support a slow sweeper's entrance, like offensive Rotom-W, specs Magnezone, or offensive Heatran. Special mention to the latter, as it deals with both straight-on counters to Serperior and to grass type switch-ins that intend to block leech seed.