Really, I don't know how you guys didn't manage to debunk the fact that Mandibuzz is
not an Mega Salamence counter.
Offensive 3 attacks MegaMence:
+1 252 Atk Aerilate Salamence Return vs. 248 HP / 252+ Def Mandibuzz: 246-291 (58.1 - 68.7%) -- guaranteed 2HKO after Leftovers recovery
+1 0- Atk Mandibuzz Foul Play vs. 0 HP / 0 Def Salamence: 202-238 (61 - 71.9%) -- guaranteed 2HKO
SubDD MegaMence:
+1 92+ Atk Aerilate Salamence Return vs. 248 HP / 252+ Def Mandibuzz: 243-286 (57.4 - 67.6%) -- guaranteed 2HKO after Leftovers recovery
+1 0- Atk Mandibuzz Foul Play vs. 168 HP / 0 Def Salamence: 198-234 (53 - 62.7%) -- guaranteed 2HKO
Mandibuzz will lose if it tries to switch in on both boosting variants of MegaMence; boosted Return 2HKOes while Foul Play fails to OHKO in turn. Mandibuzz does get one good hit off, but it will pretty much never respond to MegaMence quickly enough, compared to something like Ice Beam + Thunder Wave Cresselia (and even that isn't particularly reliable due to its Pursuit weakness and reliance on Moonlight, meaning you can't run weather on your team). I think
PikachuCandyツ is disillusioned by the fact that Mandibuzz can prevent MegaMence from setting up in its face and
win 1v1, which is a stupid thing for the MegaMence user to do in the first place.