Butterfree

Butterfree has never been a premier choice for competitive battlers, as its poor stats, hideous typing, Stealth Rock weakness, and shallow movepool have prevented it from being a decent Pokemon. However, it has become noticeably better throughout the generations: in ADV, it received Compound Eyes which remedied Sleep Powder and Stun Spore's accuracy problems, and DPP introduced Focus Sash and Choice Scarf, items that gave it more opportunities to use status moves. But while Butterfree has had a niche in the last two generations as the only Pokemon with a 97.5% accurate Sleep Powder and Stun Spore, it has never really been able to shine in the spotlight of any tier. Now, BW has once again given some useful tools which have finally given it the chance to shine. First of all, Butterfree has gained Quiver Dance, and with it, it finally has a way to sweep the opposition. Additionally, the Dream World has given Butterfree the Tinted Lens ability, which allows it to circumvent its lack of coverage and sweep with Bug Buzz. To top it all off, Venomoth is banned from RU, so Butterfree is the sole Bug-type that has access to both Quiver Dance and Sleep Powder. While Butterfree is still a poor Pokemon in many ways, and it faces stiff competition from the likes of Quiver Dancing Bug-types and Lilligant, it occupies a few niches in RU as either a reliable status spreader or a lethal Quiver Dance sweeper, and it can be very successful at those niches with a little support.