Manectric

With base 135 Speed, Manectric becomes one of the fastest Pokemon in the metagame after Mega Evolving, with very few Pokemon except Choice Scarf users able to outspeed it. It outspeeds common Pokemon such as Greninja, Mega Gengar, Mega Salamence, and Talonflame. Mega Manectric is able to lower the foe's Attack, thanks to its supportive ability Intimidate, so it can survive another hit from certain physically offensive Pokemon. This means that priority moves are less effective at KOing Mega Manectric, as most priority moves are physical. Mega Manectric has access to coverage moves such as Overheat and Hidden Power Ice in order to check or counter threats, and it can act as a nice scouter with Volt Switch, allowing it to switch out from foes that pose a huge threat. Against physical attackers not carrying a Choice Scarf, Mega Manectric's Speed allows it to attack first and Volt Switch out after lowering its foe's Attack with Intimidate. This can support a teammate in setting up against the weakened enemy. Mega Manectric is able to shut down a lot of common offensive Pokemon such as Azumarill. Unfortunately, Mega Manectric takes up a Mega slot.