With access to the picture-perfect combination of Sleep Powder, Quiver Dance, and Tinted Lens, Butterfree is perfectly capable of sweeping the opposing team. Butterfree is the only Bug-type in RU who receives the combination of Sleep Powder and Quiver Dance, and its access to Sleep Powder makes it arguably the best Bug-type Quiver Dancer in RU. While Butterfree does face some heavy competition in Lilligant, Butterfree's abilities set it apart, as Tinted Lens allows Butterfree to rely solely on Bug Buzz for coverage, freeing up room for Substitute, while Compound Eyes nearly guarantees that it Sleep Powder will hit the foe. Additionally, Butterfree is able to outspeed every unboosted Pokemon in the RU metagame after one Quiver Dance, bar Accelgor, Ninjask, and Electrode, making it difficult to revenge kill after a single boost. With little support, Quiver Dance Butterfree is very capable of freely slicing through the opposing team like a hot knife through butter.
Sleep Powder is key to this set, as Butterfree's main way to set up on an opponent is to put them to sleep. It is usually a safe option to simply throw out first when Butterfree is sent out, as BW's sleep mechanics basically guarantee that a sleeping Pokemon is effectively knocked out. However, while Sleep Powder is a key weapon in Butterfree's arsenal, note that once Butterfree has put a Pokemon to sleep, it will be unable to do so again until said Pokemon has woken up or fainted, due to Sleep Clause. As such, sometimes it is better to simply set up a Substitute instead (assuming Butterfree is facing a slower opponent), and hope the opponent switches from the threat of Sleep Powder. This allows Butterfree to save its Sleep Powder from being wasted on a Pokemon that would serve as sleep fodder, and it can then react appropriately. If the opponent merely switched in a Pokemon whom it cannot beat, such as Haze Cryogonal, Butterfree should simply use Bug Buzz to deal a little damage, then switch out. However, against other opponents, Butterfree will have a huge advantage if it has a Substitute up, as it has a variety of options at that point. This can vary from putting a dangerous Pokemon to sleep with Sleep Powder, Quiver Dancing to set up on a Pokemon who Butterfree can deal with easily, or just using Bug Buzz to deal some damage. Even if the opponent stayed in and attacked, Butterfree will only lose 25% of its health thanks to Substitute. Choosing between using Sleep Powder or using Substitute is an important choice, as it will determine how effective Butterfree will be for the rest of the match.
Quiver Dance is Butterfree's necessary boosting move, and Butterfree will quickly become difficult to deal with once it has accrued a few boosts. As Bug Buzz is a relatively decent STAB move to fall back upon, especially with Tinted Lens backing it up, Butterfree can become a considerable threat to the opponent after a single Quiver Dance. Do note however, that Butterfree's Special Attack stat is rather mediocre, so multiple Quiver Dances may be needed to sweep. Pokemon such as Moltres can wall Butterfree, so you can opt to use a coverage move such as Hidden Power Rock instead of Substitute, though keep in mind that this makes Butterfree significantly more vulnerable to priority and revenge killers.
Maximum Speed and Special Attack investment is necessary to make Butterfree as potent as possible. With the given EVs, Butterfree reaches a Speed stat of 393 after a Quiver Dance, which outspeeds everything under base 130 Speed Pokemon with maximum investment. With Butterfree's mediocre base 80 Special Attack stat, Butterfree needs to pump all its remaining EVs into Special Attack to make its Bug Buzz strong enough to actually hurt opposing Pokemon. Leftovers are the recommended item as they work well alongside Substitute and give Butterfree much needed longevity, but Life Orb gives it a significant increase in power. If you use Life Orb, though, you should use an alternative attacking option in the last slot, such as Hidden Power Ground, Psychic, Shadow Ball, or Hidden Power Flying. Tinted Lens is the preferred ability on this set as it alleviates Butterfree's issues with coverage, but Compound Eyes ensures that Sleep Powder won't miss at crucial moments.
Though Butterfree is a very capable sweeper, it has a few faults which are heavily restricting should they not be dealt with. First and foremost, Butterfree despises Stealth Rock, as it further cripples Butterfree's already poor longevity, and guarantees that Butterfree will not be able to take any hits at all. Thus, a Rapid Spinner is necessary to remove Stealth Rock so Butterfree can perform at its full potential. Kabutops and Cryogonal are good choices for this role, as they both resist some of Butterfree's weaknesses and are very bulky on either the physical or special side, respectively. Additionally, they are physical attackers, which allows them to deal with some specially defensive Pokemon who can be irksome for Butterfree to deal with, such as Cryogonal. On the flip side, Butterfree appreciates entry hazards as its Special Attack is rather average, and entry hazards guarantee some important 2HKOs and OHKOs. Spikes can be set up by the likes of Qwilfish, Ferroseed, Roselia, or Crustle, while Stealth Rock can be set up by a slew of Pokemon, including Probopass, Omastar, Sandslash, Uxie, and Steelix. Butterfree is also very frail, so moves such as Volt Switch, Baton Pass, and U-turn are useful to get it safely into the match.
The other and more troublesome issue are specially defensive Pokemon who can phaze Butterfree or KO it before it can even attempt to 2HKO them. Unfortunately, RU holds many specially defensive Pokemon who are more than happy to sponge Butterfree's attacks, such as Clefable, Cryogonal, Escavalier, Ferroseed, Gallade, Hitmonchan, Moltres, and Steelix. Though Butterfree can partially circumvent these counters via Sleep Powder, the opponent may carry more than one of these Pokemon on their team, as some of them have good synergy together. While these Pokemon are varied, for the most part, strong physical attackers are able to muscle their way through these Pokemon, paving the way for Butterfree's sweep. Aggron, Rhydon, Hitmonlee, and Crawdaunt are all capable physical attackers who can rip huge holes in these specially defensive walls. Wynaut and Magneton can also trap certain troublesome Pokemon to assist Butterfree's sweep. One can try to lure out some of these walls with another Pokemon that they commonly counter, before KOing them with a surprise move. Additionally, some offensive Pokemon can still take a hit from Butterfree after a Quiver Dance, such as Bouffalant, Drapion, and a multitude of others, so be sure to weaken the opposing team sufficiently before attempting a sweep.