Use Physical Mega Lucario. Regular Lucario is too frail, and while Mega Lucario is still frail, it has so much attack power that it will OHKO everything it touches. Lucario's middling special attack and somewhat slow speed holds it back, while Mega Lucario has enough attack and speed to sweep through teams. It even has STAB Adaptability priority in Bullet Punch. I'd try a moveset of Close Combat, Meteor Mash, Bullet Punch, and Substitute. (Meteor Mash and Bullet Punch are egg moves, other alternatives are Swords Dance and Earthquake)
Hope this helped!