Calcs time.
Thus, from the above we can gather that...
-Pinsir absolutely needs Earthquake to take on: Aegislash, Mega Aggron, Mega Ampharos, Raikou, and Doublade.
-Pinsir can get get away with CC to take on: Heatran, Magnezone, Metagross (using +2 Return instead of +2 CC), and Carbink.
-The choice of EQ vs CC is iffy when dealing with: Mega Mawile (depends on when it mega evolved), Jirachi (depends on set), and Mega Manectric (depends on when it mega evolved).
-Pinsir loses either way to: Klefki (Pinsir will always be crippled).
And yeah, I noticed at the last second that I accidentally did my calcs with 4/0 Pinsir instead of 0/0 Pinsir. Doesn't really make a difference, though.
Code:
Klefki
252 Atk Pinsir Earthquake vs. 252 HP / 152+ Def Klefki: 210-248 (66 - 77.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Pinsir Close Combat vs. 252 HP / 152+ Def Klefki: 125-148 (39.3 - 46.5%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Pinsir Quick Attack vs. 252 HP / 152+ Def Klefki: 41-48 (12.8 - 15%) -- possibly the worst move ever
Verdict: Pinsir won't be able to beat Klefki with either option before it gets Thunder-Waved.
Mega Mawile
+1 252 Atk Pinsir Earthquake vs. 252 HP / 0 Def Mega Mawile: 308-364 (101.3 - 119.7%) -- guaranteed OHKO
+1 252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Mega Mawile: 185-218 (60.8 - 71.7%) -- guaranteed 2HKO after Stealth Rock
+2 252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Mega Mawile: 246-290 (80.9 - 95.3%) -- 12.5% chance to OHKO after Stealth Rock
+3 252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Mega Mawile: 307-362 (100.9 - 119%) -- guaranteed OHKO
+2 252 Atk Aerilate Pinsir Quick Attack vs. 252 HP / 0 Def Mega Mawile: 80-94 (26.3 - 30.9%) -- guaranteed 4HKO after Stealth Rock
252+ Atk Mega Mawile Play Rough vs. 4 HP / 0 Def Pinsir: 237-280 (87.1 - 102.9%) -- 18.8% chance to OHKO
252+ Atk Mega Mawile Sucker Punch vs. 4 HP / 0 Def Pinsir: 141-167 (51.8 - 61.3%)
Verdict: Without EQ, Pinsir risks the OHKO by Play Rough. However, if you predict a Sucker Punch then you can attempt another SD for a clean OHKO with +3 CC. It should be noted that what I just said applies for a situation where regular Mawile switched in on a SD and then Mega evolved. Should Mega Mawile switch in on the SD having previously mega evolved, then it risks a OHKO from +2 CC.
Heatran
252 Atk Pinsir Close Combat vs. 0 HP / 0 Def Heatran: 284-336 (87.9 - 104%) -- guaranteed OHKO after Stealth Rock
252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Heatran: 284-336 (73.5 - 87%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 Atk Aerilate Pinsir Quick Attack vs. 252 HP / 0 Def Heatran: 46-55 (11.9 - 14.2%) -- possibly the worst move ever
Verdict: Heatran cannot take on Pinsir, except if it has a scarf and switches in on Return/Quick Attack. Even if Close Combat on the switch doesn't OHKO Scarf-tran, Quick Attack will do the lava monster in.
Magnezone
252 Atk Pinsir Close Combat vs. 172 HP / 0 Def Magnezone: 264-312 (81.4 - 96.2%) -- 18.8% chance to OHKO after Stealth Rock
252 Atk Pinsir Close Combat vs. 4 HP / 0 Def Magnezone: 264-312 (93.6 - 110.6%) -- 93.8% chance to OHKO after Stealth Rock
Verdict: Magnezone gets wrecked by Close Combat + QA.
Mega Aggron
+2 252 Atk Pinsir Earthquake vs. 252 HP / 16+ Def Mega Aggron: 160-189 (46.5 - 54.9%) -- 98.8% chance to 2HKO after Stealth Rock
+2 252 Atk Pinsir Close Combat vs. 252 HP / 16+ Def Mega Aggron: 192-226 (55.8 - 65.6%) -- guaranteed 2HKO after Stealth Rock
+4 252 Atk Pinsir Earthquake vs. 252 HP / 16+ Def Mega Aggron: 240-283 (69.7 - 82.2%) -- guaranteed 2HKO after Stealth Rock
+4 252 Atk Pinsir Close Combat vs. 252 HP / 16+ Def Mega Aggron: 288-339 (83.7 - 98.5%) -- 31.3% chance to OHKO after Stealth Rock
0+ Atk Mega Aggron Heavy Slam (120 BP) vs. 4 HP / 0 Def Pinsir: 162-192 (59.5 - 70.5%) -- guaranteed 2HKO
0+ Atk Mega Aggron Heavy Slam (120 BP) vs. -1 4 HP / 0 Def Pinsir: 244-288 (89.7 - 105.8%) -- 37.5% chance to OHKO
Verdict: Pinsir needs EQ and SR to take on Mega Aggron (SD on the switch in, followed by two Earthquakes), and even then it needs Mega Aggron to lack Rock Slide. Attempting to do the same with Close Combat means Pinsir risks the OHKO by Heavy Slam.
Jirachi
+2 252 Atk Pinsir Close Combat vs. 0 HP / 0 Def Jirachi: 298-351 (87.3 - 102.9%) -- 56.3% chance to OHKO after Stealth Rock
+2 252 Atk Pinsir Earthquake vs. 0 HP / 0 Def Jirachi: 498-586 (146 - 171.8%) -- guaranteed OHKO
0 SpA Jirachi Thunderbolt vs. 4 HP / 0 SpD Pinsir: 174-206 (63.9 - 75.7%) -- guaranteed OHKO after Stealth Rock
252 Atk Jirachi Fire Punch vs. 4 HP / 0 Def Pinsir: 118-140 (43.3 - 51.4%) -- 18.8% chance to OHKO after Stealth Rock
Verdict: Close Combat + QA can beat Scarf-rachi, but not always if Pinsir is at half-health. Pinsir w/ CC loses to SubCM Jirachi.
Metagross
+2 252 Atk Pinsir Earthquake vs. 252 HP / 0 Def Metagross: 396-468 (108.7 - 128.5%) -- guaranteed OHKO
+2 252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Metagross: 238-280 (65.3 - 76.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+2 252 Atk Aerilate Pinsir Return vs. 252 HP / 0 Def Metagross: 197-232 (54.1 - 63.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Metagross Meteor Mash vs. -1 4 HP / 0 Def Pinsir: 213-252 (78.3 - 92.6%) -- guaranteed OHKO after Stealth Rock
252+ Atk Metagross Bullet Punch vs. -1 4 HP / 0 Def Pinsir: 94-112 (34.5 - 41.1%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Metagross Meteor Mash vs. 4 HP / 0 Def Pinsir: 142-168 (52.2 - 61.7%) -- guaranteed OHKO after Stealth Rock
252+ Atk Metagross Bullet Punch vs. 4 HP / 0 Def Pinsir: 64-76 (23.5 - 27.9%) -- 76.6% chance to 2HKO after Stealth Rock
Verdict: Earthquake is the better option. If Pinsir uses CC, it gets picked off by Meteor Mash + Bullet Punch. However, a full-health Pinsir can beat Metagross if it uses Return instead of CC.
Carbink
Verdict: No calcs necessary. +2 Pinsir 2HKOs Carbink no matter which option, and Carbink can't hit back hard enough with Moonblast.
Mega Ampharos
+2 252 Atk Pinsir Earthquake vs. 252 HP / 0 Def Mega Ampharos: 476-562 (123.9 - 146.3%) -- guaranteed OHKO
+2 252 Atk Pinsir Close Combat vs. 252 HP / 0 Def Ampharos: 286-337 (74.4 - 87.7%) -- 6.3% chance to OHKO after Stealth Rock
252+ SpA Ampharos Volt Switch vs. 4 HP / 0 SpD Pinsir: 404-476 (148.5 - 175%) -- guaranteed OHKO
Verdict: Earthquake is needed to reliably beat Mega Ampharos. 6.3% chance to OHKO with +2 CC isn't good enough.
Mega Manectric
-1 252 Atk Pinsir Earthquake vs. 0 HP / 4 Def Mega Manectric: 198-234 (70.4 - 83.2%) -- guaranteed 2HKO after Stealth Rock
-1 252 Atk Pinsir Close Combat vs. 0 HP / 4 Def Mega Manectric: 119-141 (42.3 - 50.1%) -- 93.4% chance to 2HKO after Stealth Rock
252 Atk Pinsir Close Combat vs. 0 HP / 4 Def Manectric: 224-264 (79.7 - 93.9%) -- 43.8% chance to OHKO after Stealth Rock
-1 252 Atk Aerilate Pinsir Quick Attack vs. 0 HP / 4 Def Mega Manectric: 39-46 (13.8 - 16.3%) -- possible 6HKO after Stealth Rock
Verdict: If Manectric has already mega evolved before switching in, then Pinsir can only beat it with EQ on the switch followed by QA. However, regular Manectric cannot switch into +0 CC as it will be picked off by QA on the next turn. Pinsir always loses if it uses SD or Return on the switch in.
Raikou
252 Atk Pinsir Earthquake vs. 4 HP / 0 Def Raikou: 316-372 (98.1 - 115.5%) -- guaranteed OHKO after Stealth Rock
252 Atk Pinsir Close Combat vs. 4 HP / 0 Def Raikou: 189-223 (58.6 - 69.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Verdict: Pinsir only wins if it uses EQ on the switch-in.
-Pinsir absolutely needs Earthquake to take on: Aegislash, Mega Aggron, Mega Ampharos, Raikou, and Doublade.
-Pinsir can get get away with CC to take on: Heatran, Magnezone, Metagross (using +2 Return instead of +2 CC), and Carbink.
-The choice of EQ vs CC is iffy when dealing with: Mega Mawile (depends on when it mega evolved), Jirachi (depends on set), and Mega Manectric (depends on when it mega evolved).
-Pinsir loses either way to: Klefki (Pinsir will always be crippled).
And yeah, I noticed at the last second that I accidentally did my calcs with 4/0 Pinsir instead of 0/0 Pinsir. Doesn't really make a difference, though.