Mawile

While Mega Mawile has the highest Attack stat in the game, its middling Speed and poor dual STAB coverage mean that it struggles with wallbreaking, contrary to what its Attack stat would suggest. In particular, it is completely stopped by Primal Groudon, which resists both of Mawile's STAB moves and can outspeed it. Mega Mawile's niche is largely in checking some specific special attackers with its fantastic defensive typing while being able to gain momentum with Baton Pass, allowing it to switch out of the Pokemon that it cannot harm.