>>32953680252 Atk Aerilate Pinsir-Mega Quick Attack vs. 0 HP / 0 Def Marshadow: 218-258 (67.9 - 80.3%) -- guaranteed 2HKO
252 Atk Marshadow Spectral Thief vs. 0 HP / 0 Def Pinsir-Mega: 123-145 (45.3 - 53.5%) -- 41% chance to 2HKO
If it was damaged previously, sure it can take care of the job. However, if Pinsir couldn't kill and it was damaged by rocks, then it dies next turn:
252 Atk Marshadow Shadow Sneak vs. 0 HP / 0 Def Pinsir-Mega: 55-66 (20.2 - 24.3%) -- guaranteed 5HKO
It's even worse if it stole an attack boost. Actually, if you have Z-Spectral and has good HP, you don't even need to boost in order to almost reliably oneshot it:
252 Atk Marshadow Soul-Stealing 7-Star Strike vs. 0 HP / 0 Def Pinsir-Mega: 265-313 (97.7 - 115.4%) -- 87.5% chance to OHKO
