Raikou

On paper, it can seem as though there is no reason to use Raikou over Mega Manectric, which has higher Special Attack and Speed, Fire-type coverage, and Intimidate. However, Raikou has more special bulk, allows the use of another Mega Pokemon, has access to Light Screen and Reflect, and is a better user of Snarl, which Mega Manectric struggles to fit it onto its moveset. Raikou, on the other hand, has a slot free for coverage moves or Snarl and has more special bulk to survive hits so it can keep on using Snarl. Although Mega Manectric has a higher Speed, Raikou's base Speed of 115 is still incredible, outspeeding other popular Electric-types such as Zapdos and Thundurus. Unlike the latter two, however, Raikou has a weakness to Ground, which is not helped by the extreme popularity of Choice Scarf Landorus-T.