I've been waiting for this:
EVs: 4 HP/252 Atk/252 Spe
Ability: Hyper Cutter
Mega Pinsir is only 4HKOed at best by Marshtomp's Waterfall and Double-Edge; it's also immune to Earthquake and takes a pittance from Brick Break. Even unboosted, Aerilate Return does a lot to Marshtomp and it's an OHKO when Mega Pinsir is at +2 Attack.
And just saying, but running Adamant with barely any Attack EVs at all is a waste.