252+ Atk Mega Pinsir Earthquake vs. 252 HP / 0 Def Aegislash-Shield: 192-228 (59.2 - 70.3%) -- guaranteed 2HKOHe asked for a pros and cons list. I've played this game before, and used mega pinsir, I can assure you. I tried to put it in terms that someone who's new to the game. Pinsir needs +2 to even touch stuff like skarmory, aegislash, etc. Earthquake hits aegislash, but makes skarmory a counter, and vice versa. His movepool is small, and lacks coverage. That's bad, but can be worked around.
Well then, i sure dont know what kind of aegislash are you facing. Flying+Ground is excellent coverage, specially when it can burst through resists with a swords dance boost. Even rotom-w is taking 61% minimum from a boosted return. The only thing that can switch in consistently in it is skarmory, and thats only because it has stab brave bird.