Serperior

Thanks to Contrary, Serperior can utilize its powerful Leaf Storm and simultaneously boost its Special Attack by two stages, allowing it to quickly break down opposing walls. Serperior's high base 113 Speed allows it to outpace threats such as Mega Diancie, Kitsunoh, and Latias, making it a potent late-game cleaner once it obtains a boost from Leaf Storm. Serperior can also put heavy pressure on stall teams; Pokemon with Unaware such as Arghonaut, Quagsire, and Clefable can't safely switch into a Life Orb-boosted Leaf Storm, and Serperior can bypass some of its would-be checks depending on which Hidden Power it runs. However, Serperior's reliance on Hidden Power for coverage means that once the opponent knows which Hidden Power Serperior is running, walling it becomes an easier task. Also, outside of Serperior's high Speed, the rest of its stats are somewhat disappointing. For instance, its base 75 Special Attack is rather unimpressive without a boost. Serperior is also quite prone to being revenge killed by faster threats and priority users such as Talonflame, Syclant, and various Choice Scarf users due to its middling bulk and mediocre defensive typing. Serperior's opportunities to switch in are rather limited; taking too much damage while switching in coupled with Life Orb recoil can leave it even more susceptible to being revenge killed.