Pikachu

With its signature item, Light Ball, Pikachu might seem like an incredibly dominating threat with offensive stats rivaling some Ubers; however, there are far too many things holding Pikachu back from being effective. Pikachu's main downfall should be fairly obvious: its bulk is absolutely pathetic--even lower than the likes of Haunter or Kadabra. While Pikachu can mitigate its frailty somewhat with Substitute, Encore, and its ability, Lightning Rod, its second downfall isn't as easy to overlook. The very Light Ball that makes Pikachu viable is also what makes it so limited; as Pikachu needs its Light Ball to not be complete dead weight, it is unable to use any other item, including Life Orb and all Choice items. Thus, Pikachu will not hit as hard as you might think it would: traditional powerhouses greatly depend on the boosts these items provide, while Pikachu has to do without. Successfully using Pikachu will require massive amounts of team support and top-level prediction.