Ariados

At first glance, Ariados appears nearly useless; its typing is both common and poor, giving it redundant STAB coverage and a weakness to Stealth Rock. Its stats are all mediocre except for its Attack, and even then it lacks the physical movepool to take advantage of it. It's hard to imagine why anyone would want to use Ariados given these flaws, but it does have one thing going for it: it is one of only two Pokemon in UU capable of Baton Passing a trapping move. Successfully trapping an opponent whom one of your Pokemon can set up on will often lead to an easy victory. Access to Toxic Spikes and a useful ability in Insomnia gives Ariados further value as a supporting Pokemon. It can't do much on its own, but on a team built around its strengths, Ariados is nigh-irreplaceable.