Blaziken - It's in Ubers, so at first glance it's clearly very strong. It has great type coverage and a humongous Attack stat when in Mega (160), combined with a decent Speed stat of 100. However, the real niche of Blaziken in Ubers is it's Mega and Hidden Ability: Speed Boost. If Blaziken can Protect turn 1 and acquire a Speed Boost, it can outspeed a large portion of the unboosted Tier if it's in Mega (Deoxys-S and a few others outspeed Mega-Blaziken). Coupled with his coverage of Fire, Fighting and Rock to hit most of the tier for neutral/super-effective damage. If a Swords Dance can be made, Blaziken becomes a terrifying sweeper or wallbreaker.
Greninja - Also in Ubers, it sadly has downsides when played offensively, but it's game-changing Hidden Ability Protean allows it to find a role in this immensely dangerous tier as an amazing suicide lead. The ability to set up both Spikes and Toxic Spikes is much appreciated, as well as Taunt to block Defog and Protean Shadow Sneak to block Rapid Spin. Greninja also has the speed to perform well.
Seperior - At first glance, Serperior looks underwhelming... Until you see it's Hidden Ability Contrary. Able to become a deadly sweeper thanks to it's superior speed and Leaf Storm now INCREASING its Special Attack +2. It also has some relatively nice bulk so it can take a few hits too.
Infernape - It's in UU, but can act as a very good wallbreaker in OU. It has quite fast, plus with the Life Orb it can deal heavy damage to most of the Pokemon in OU.