So far haven't been so awed with mence. It's defensive typing is pretty shabby with ninja and drill on every team, and it just doesn't have the power to be as threatening as say, mega-luc. Overall, I'd say it wreaks unprepared teams, but it just doesn't seem OP to me. Unhealthy for the meta, maybe (probably), but not OP. Have yet to try dedicated bulky DD mence and mixmence yet, but all out offensive doesn't look to be good as a stand-alone sweeper. Maybe add talon and a wish/healing wish mon and it'll probably outclass m-pinsir. IDK if I'm not using it right, but I just don't see the great uncheckable, uncounterable beast that lives in others' eyes.
Greninja, though. Gunk shot, spikes (FU thundy), low kick... This thing has won so many games. It's just ridiculous.
Won't speak on Greninja, but Drill can't beat Salamence without support.
252 Jolly Drill falls 1 point short of MegaMence's uninvested positive-nature speed, and Mence's investment almost always puts it on top.
Defensive/Bulky Mence
252+ Atk Life Orb Excadrill Rock Slide vs. 252 HP / 252 Def Salamence: 161-190 (40.8 - 48.2%) -- guaranteed 3HKO
252+ Atk Life Orb Excadrill Rock Slide vs. 252 HP / 252+ Def Salamence: 146-172 (37 - 43.6%) -- guaranteed 3HKO
0 Atk Aerilate Salamence Return vs. 0 HP / 4 Def Excadrill: 148-174 (40.9 - 48.1%) -- guaranteed 3HKO
Since Mence goes first, it almost always beats Drill factoring in a round of LO recoil
Offensive Mence
252+ Atk Life Orb Excadrill Rock Slide vs. 0 HP / 0- Def Salamence: 213-252 (64.3 - 76.1%) -- guaranteed 2HKO
-1 252+ Atk Life Orb Excadrill Rock Slide vs. 0 HP / 0- Def Salamence: 143-169 (43.2 - 51%) -- 3.1% chance to 2HKO (Intimidate)
252 Atk Aerilate Salamence Return vs. 0 HP / 4 Def Excadrill: 177-208 (49 - 57.6%) -- 95.7% chance to 2HKO
252+ Atk Aerilate Salamence Return vs. 0 HP / 4 Def Excadrill: 194-228 (53.7 - 63.1%) -- guaranteed 2HKO
A bit more iffy, but this is assuming Mence has no coverage, which offensive WILL have
252 Atk Salamence Earthquake vs. 0 HP / 4 Def Excadrill: 356-420 (98.6 - 116.3%) -- 87.5% chance to OHKO
0 SpA Salamence Fire Blast vs. 0 HP / 0 SpD Excadrill: 262-310 (72.5 - 85.8%) -- guaranteed 2HKO
Drill can't beat MegaMence unless it has sand for residual and outspeed, but considering Hippo is passive set-up fodder and Tyranitar w/out an Ice move
0 SpA Tyranitar Ice Beam vs. 0 HP / 0 SpD Salamence: 272-324 (82.1 - 97.8%) -- guaranteed 2HKO after sandstorm damage
0 Atk Tyranitar Ice Punch vs. 0 HP / 0- Def Salamence: 248-296 (74.9 - 89.4%) -- guaranteed 2HKO after sandstorm damage
252 Atk Salamence Earthquake vs. 248 HP / 252+ Def Tyranitar: 160-190 (39.7 - 47.1%) -- guaranteed 3HKO after Leftovers recovery
+1 252 Atk Salamence Earthquake vs. 248 HP / 252+ Def Tyranitar: 238-282 (59 - 69.9%) -- guaranteed 2HKO after Leftovers recovery
Any residual damage and/or boosts means T-tar can't switch in without being sacked.