NOTE: Whenever I refer to Mega Pinsir's Feint or show it in calcs it means Return'd Feint (aka 102 BP). All calcs against Mega Pinsir are with their normal BP, unless I say "Return'd" in the calc.
Physically defensive Zapdos is one of the best Mega Pinsir checks. At +2, Feint can't OHKO even with Rocks, and Return'd Volt Switch is a clean OHKO.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 248 HP / 176+ Def Zapdos: 212-250 (55.3 - 65.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
68 SpA Zapdos Return'd Volt Switch vs. 0 HP / 4 SpD Mega Pinsir: 306-362 (112.9 - 133.5%) -- guaranteed OHKO
It also has access to Defog and Roost for utility and reliable recovery.
Ayyyy sweg keys. This isn't the
best check as it kinda relies on paralyzing the opp :/ Klefki can take a +2 Feint tho and TWave, OR it can set Reflect to make something else tank the +2 Feint easier. It also sets Spikes, and hazard stacking is actually ridiculously effective in this meta tbh.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 248 HP / 252+ Def Klefki: 189-222 (59.6 - 70%) -- guaranteed 2HKO after Leftovers recovery
Doublade is another of the best checks to Mega Pinsir. It takes +2 Feint like it's nothing, and has powerful priority of its own. It can tank a +2 EQ, and Return'd Shadow Sneak 2HKOs.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 240 HP / 0 Def Eviolite Doublade: 116-137 (36.3 - 42.9%) -- guaranteed 3HKO
+2 252 Atk Mega Pinsir Earthquake vs. 240 HP / 0 Def Eviolite Doublade: 234-276 (73.3 - 86.5%) -- guaranteed 2HKO
252+ Atk Doublade Return'd Shadow Sneak vs. 0 HP / 0 Def Mega Pinsir: 139-165 (51.2 - 60.8%) -- guaranteed 2HKO
252+ Atk Doublade Gyro Ball (126 BP) vs. 0 HP / 0 Def Mega Pinsir: 172-204 (63.4 - 75.2%) -- guaranteed 2HKO [0 Speed EVs, Brave nature, 0 Speed IVs Doublade vs. 252 Speed EVs, Jolly nature Mega Pinsir]
A more offensive check to Mega Pinsir. Either can take a +2 Feint and KO after one round of pre-Mega Stealth Rock damage with Return'd Bullet Punch (if Choice Band Adamant Metagross and Adamant Mega Metagross respectively).
+2 252 Atk Aerilate Mega Pinsir Feint vs. 252 HP / 0 Def Metagross: 197-232 (54.1 - 63.7%) -- guaranteed 2HKO
252+ Atk Choice Band Metagross Return'd Bullet Punch vs. 0 HP / 0 Def Mega Pinsir: 241-285 (88.9 - 105.1%) -- 31.3% chance to OHKO
+2 252 Atk Aerilate Mega Pinsir Feint vs. 0 HP / 4 Def Mega Metagross: 174-204 (57.8 - 67.7%) -- guaranteed 2HKO
252+ Atk Tough Claws Mega Metagross Return'd Bullet Punch vs. 0 HP / 0 Def Mega Pinsir: 220-261 (81.1 - 96.3%) -- guaranteed 2HKO
All the Rotom formes except Mow work tbh, but these are the most viable. They can tank +2 Feint or CC and proceed to burn Mega Pinsir with Will-O-Wisp or KO it with Return'd Volt Switch after one round of pre-Mega Stealth Rock damage.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 248 HP / 252+ Def Rotom-W/Rotom-H: 169-200 (55.7 - 66%) -- guaranteed 2HKO after Leftovers recovery
+2 252 Atk Mega Pinsir Close Combat vs. 248 HP / 252+ Def Rotom-W/Rotom-H: 204-241 (67.3 - 79.5%) -- guaranteed 2HKO after Leftovers recovery
0 SpA Rotom-W/Rotom-H Return'd Volt Switch vs. 0 HP / 4 SpD Mega Pinsir: 252-296 (92.9 - 109.2%) -- 56.3% chance to OHKO
The counter is here o3o. It isn't 2HKOd by +2 Feint (as long as rocks aren't on the field), although +2 CC can 2HKO. It can phaze with Whirlwind (so you should run hazards) and if it takes enough damage from Rocks (1 round of Stealth Rock damage post-Mega or two rounds either Mega or non-Mega) then Brave Bird (or Return'd Drill Peck if you don't want the recoil) can KO it.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 252 HP / 252+ Def Skarmory: 140-165 (41.9 - 49.4%) -- guaranteed 3HKO after Leftovers recovery
+2 252 Atk Mega Pinsir Close Combat vs. 252 HP / 252+ Def Skarmory: 170-200 (50.8 - 59.8%) -- 89.1% chance to 2HKO after Leftovers recovery
0 Atk Skarmory Return'd Drill Peck vs. 0 HP / 0 Def Mega Pinsir: 156-186 (57.5 - 68.6%) -- guaranteed 2HKO
0 Atk Skarmory Brave Bird vs. 0 HP / 0 Def Mega Pinsir: 186-218 (68.6 - 80.4%) -- guaranteed 2HKO
+
For an offensive team, this is a neat duo that takes out Mega Pinsir. Endure Tankchomp makes Mega Pinsir take 7/12 of its HP in recoil, and Endure outprioritizes Feint. Then, LO Weavile with Return'd Feint can come in, outspeed Mega Pinsir and kill it with Feint. If it hasn't boosted yet, Chomp can phaze it with Dragon Tail.
252 Atk Life Orb Weavile Return'd Feint vs. 0 HP / 0 Def Mega Pinsir: 117-139 (43.1 - 51.2%) -- 4.7% chance to 2HKO
7/12*100%=58.3%+43.1%=101.4% so even the lowest possible roll kills.
Choice Scarf Magnezone and Magneton (both of whom receive a buff with 102 BP HP Fire I might add) can both revenge kill Mega Pinsir. They 4x resist Feint, so they take it with ease and OHKO with Thunderbolt (or Volt Switch/Return'd HP Fire after one round of pre-Mega Rocks).
+2 252 Atk Aerilate Mega Pinsir Feint vs. 0 HP / 4 Def Magnezone: 109-129 (38.7 - 45.9%) -- guaranteed 3HKO after Stealth Rock
252 SpA Magnezone Thunderbolt vs. 0 HP / 4 SpD Mega Pinsir: 320-380 (118 - 140.2%) -- guaranteed OHKO
+2 252 Atk Aerilate Mega Pinsir Feint vs. 0 HP / 4 Def Magneton: 128-151 (53.1 - 62.6%) -- guaranteed 2HKO after Stealth Rock
252 SpA Magneton Thunderbolt vs. 0 HP / 4 SpD Mega Pinsir: 306-360 (112.9 - 132.8%) -- guaranteed OHKO
ScarfTar is another excellent revenge killer, as it can tank a +2 Feint uninvested and proceed to OHKO it back with Stone Edge.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 0 HP / 4 Def Tyranitar: 227-267 (66.5 - 78.2%) -- guaranteed 2HKO after Stealth Rock
Stone Edge obviously OHKOs :/
Physically defensive Hippowdon can take one boosted hit and if it carries Stone Edge or Return'd Rock Tomb (the better overall utility option imo, as the only other attack you'd really want is EQ, and that's already 100 BP) it can OHKO in return.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 252 HP / 252+ Def Hippowdon: 318-375 (75.7 - 89.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
4 Atk Hippowdon Rock Tomb vs. 0 HP / 0 Def Mega Pinsir: 280-332 (103.3 - 122.5%) -- guaranteed OHKO
Lando-T can also check Mega Pinsir from full health. The defensive set has a very good chance to live a +1 Feint (SD + Intim) after Rocks, and it is guaranteed to live without Rocks, while it KOs back with Stone Edge (or Return'd Smack Down, which is a neat and likely superior option).
+1 252 Atk Aerilate Mega Pinsir Feint vs. 252 HP / 252+ Def Landorus-T: 286-337 (74.8 - 88.2%) -- 6.3% chance to OHKO after Stealth Rock
0 Atk Landorus-T Stone Edge vs. 0 HP / 0 Def Mega Pinsir: 340-404 (125.4 - 149%) -- guaranteed OHKO
0 Atk Landorus-T Return'd Smack Down vs. 0 HP / 0 Def Mega Pinsir: 348-412 (128.4 - 152%) -- guaranteed OHKO
Scarf Ditto obviously revenge kills Mega Pinsir. It outspeed due to Scarf, and I don't even need to calc Feint easily OHKOing Mega Pinsir as you've seen it do a ton to resists--mons weak to Flying don't stand a chance lmao. Probably the best revenge killer, especially if you have Mega Pinsir too, as this weakens their Mega Pinsir check/counter.
Mega Manectric can check Mega Pinsir as long as Rocks aren't up. It can take a +1 (after Swords Dance and Intimidate) Feint, and OHKO back with Thunderbolt (or Volt Switch after one round of pre-Mega Stealth Rock damage).
+1 252 Atk Aerilate Mega Pinsir Feint vs. 0 HP / 4 Def Mega Manectric: 222-261 (79 - 92.8%) -- guaranteed 2HKO
252 SpA Mega Manectric Thunderbolt vs. 0 HP / 4 SpD Mega Pinsir: 330-390 (121.7 - 143.9%) -- guaranteed OHKO
Standard specially defensive Mega Ampharos can also check Mega Pinsir that lack EQ. It can take a +2 Feint after Stealth Rock and OHKO back with Return'd Volt Switch.
+2 252 Atk Aerilate Mega Pinsir Feint vs. 248 HP / 0 Def Ampharos: 283-333 (73.8 - 86.9%) -- guaranteed 2HKO
28 SpA Ampharos Volt Switch vs. 0 HP / 4 SpD Mega Pinsir: 276-326 (101.8 - 120.2%) -- guaranteed OHKO