My issue with Meg Gar is that it loses Levitate, making it incredibly brittle to the common offensive move found in Earthquake, replacing a very useful resistance with a weakness. Not to mention the poison can now counter the new Fairy type for pokemon like Sylveon and Azumaril.
Umm...don't switch in on anything that has Earthquake? Shadow Tag is 100000000000 times better than Levitate on a Pokemon like Mega Gengar. If used correctly, it gets at least two kills per match unless your opponent is running something like Tyranitar/Chansey/Blissey/Assault Vest Specially Defensive Hippowdon/(you get the point)
Also, what happened to Goodra? Rain Dance + Rest + Damp Rock + Hydration can stall like nobody's business.
Goodra wastes an item slot it could be using for passive recovery in Leftovers, forgoes Gooey, which slows down physical attackers, and wastes two moveslots on Rain Dance+Rest. If you use a strong physical attack on it, it will crumble, and Hydration+Rest cannot fix that.
I've found it quite useful on Showdown, especially being able to team it up with Hurricane Volcanora as a switch-in. The other two moves are 100% Thunder and STAB Dragon Pulse, which offer great coverage against potential threats, and both are standard effective on T-Tar which I've found to be the main issue.
252+ SpA Goodra Dragon Pulse vs. 0 HP / 0 SpD Tyranitar in RAIN: 144-171 (42.22 - 50.14%) -- 0.39% chance to 2HKO
Hahahahahahahahahahahaha
While that's a very valid point I honestly haven't seen many Mawile. As said earlier, the thing I fear is Mega Kahn, to which I accept my defeat instantly, as it just can Sucker Punch everything to death.
Mega Mawile is a viable Pokemon in OU. It has 678 Attack if using an Adamant nature, and it can use Swords Dance, which makes its Attack insane. Also Mega Mawile uses Sucker Punch a lot better than Mega Kangaskhan:
+2 252+ Atk Huge Power Mega Mawile Sucker Punch vs. 252 HP / 252+ Def (custom): 340-401 (96.31 - 113.59%) -- 75% chance to OHKO
+2 252+ Atk Parental Bond Mega Kangaskhan Sucker Punch vs. 252 HP / 252+ Def (custom): 289-340 (81.86 - 96.31%) -- guaranteed 2HKO
Goodra @ Damp Rock
Hydration
Calm 252 HP/ 114 Def/ 112 Spd/ 32 SpA
- Rest
- Rain Dance
- Thunder
- Dragon Pulse
That's even worse, it can't hope to do jack shit with its attacks:
32 SpA Goodra Thunder vs. 248 HP / 156 SpD Gyarados: 332-392 (84.47 - 99.74%) -- guaranteed 2HKO
32 SpA Goodra Dragon Pulse vs. 252 HP / 252+ SpD Multiscale Dragonite: 75-88 (19.43 - 22.79%) -- possible 6HKO (actually a 4HKO...lol)
Not to mention:
252+ Atk Iron Fist Conkeldurr Ice Punch vs. 252 HP / 112 Def Goodra: 310-366 (87.81 - 103.68%) -- guaranteed OHKO after Stealth Rock
252 SpA Choice Specs Latios Draco Meteor vs. 252 HP / 112+ SpD (custom): 440-522 (124.64 - 147.87%) -- guaranteed OHKO
252 SpA Protean Greninja Ice Beam vs. 252 HP / 112+ SpD Goodra: 168-200 (47.59 - 56.65%) -- guaranteed 2HKO after Stealth Rock