Mega Latios is king of physical setup sweeping IMO. 130/160/120 bulk is nothing to laugh at (barring Ice-type special attacks and Regice), so he can probably DD up with impunity (although this meta has some seriously absurd offensive stats running around occasionally). And he has base 130 Attack to start with, which isn't too shabby but is basically "okay" in stat swap. And he has Roost/Recover. You could even add Refresh on to that if you think he's strong enough to go mono-attacker.
Except Regice exists.
Non-Mega Latios is definitely a defensive mon with good 130/130/110 bulk. He can set screens, recover, refresh, defog, tailwind, TWave, Toxic, and trap with Whirlpool. Problem is, he can't do all that at once. If he could screens, recover, refresh, Toxic, AND Whirlpool, Latios would quite possibly be a very happy Pokémon.
Again, except Regice. lol.
Standard Latias has a niche over Mega Latios in her access to Sucker Punch for priority, which might make Band Latias a thing, especially since she doesn't take up your Mega slot. She's got a fair number of other physical moves to work with too: Dragon Claw/Outrage, Zen Headbutt, Waterfall, Earthquake, and even Steel Wing and Shadow Claw if you're desperate. And she can BandTrick people if you want to.
As for Mega Latias, she can run mixed with some effectiveness but lacks the Attack boost of a Band, making her weaker overall. She can run Hone Claws though (which also fixes Zen Headbutt, Draco Meteor, and Steel Wing accuracy), but I doubt that's really all that worthwhile. But again, Sucker Punch priority. She also might be useful as a healer with offensive presence as 130 base HP makes pretty big Wishes, at least as far as standard OU is concerned (they might be underwhelming for this crazy meta though). (And realistically 130/120/100 is probably still pretty respectable bulk.)
Regice is freaking insane. I don't think anything short of Mega Diancie can tank a banded Ice Punch (she can live 3 of them with no investment OMG). (I was wrong, there are other things that can.) And for that, there's Iron Head.
252+ Atk Choice Band Regice Ice Punch vs. 0 HP / 0 Def (Mega) Diancie: 186-220 (42.1 - 49.8%) -- guaranteed 3HKO
Behold the Queen of Stat Switch!
But at the same time, Regice only has to run 100 Speed EVs to be able to outspeed a max speed Mega Diancie, and then it still gets to run Adamant.
She can tank a single Iron Head if she runs full defensive...
252+ Atk Choice Band Regice Iron Head vs. 248 HP / 252+ Def (Mega) Diancie: 412-488 (81.9 - 97%) -- guaranteed 2HKO
But then she can't really do enough damage back.
8 SpA (Mega) Diancie Ancient Power vs. 156 HP / 0 SpD Regice: 246-290 (72.3 - 85.2%) -- guaranteed 2HKO
(And yes, with no Attack or Sp. Atk investment and a neutral nature in both, Ancient Power really does hit Regice harder than Diamond Storm does.)
Also Regice doesn't even have to run Iron Head to take her out.
252+ Atk Choice Band Regice Earthquake vs. 248 HP / 252+ Def (Mega) Diancie: 258-304 (51.2 - 60.4%) -- guaranteed 2HKO
As for things that can actually tank Regice...
Well, Arcanine sure can't thanks to Clear Body blocking Intimidate.
Chansey can stop it though. Sure, she takes a boatload from Hammer Arm, but she also heals back up with Drain Punch. That said, even Chansey only beats it 1v1. (Or she can come in when it's locked into a move she can tank, like anything that isn't Hammer Arm or Superpower, and then whack something with her 250 base Attack as they switch.)
Physically defensive Genesect outright counters Regice provided Stealth Rock isn't up.
252+ Atk Choice Band Regice Earthquake vs. 248 HP / 252+ Def Genesect: 186-219 (41.9 - 49.4%) -- guaranteed 3HKO after Leftovers recovery
Meanwhile...
+1 8 SpA Genesect Flash Cannon vs. 156 HP / 0 SpD Regice: 342-404 (100.5 - 118.8%) -- guaranteed OHKO
The +1 is from Download, obviously. As for whether or not a physically-defensive Genesect is good for anything else, well, IDK. Download can make even base 71 offences good enough to deal with especially fragile sweepers if you have proper coverage, though.
Also, Carbink seems like a good one- or two-use revenge killer thanks to Sturdy and its amazing 150 base Speed. Stick a Scarf on it (yeah, Scarf and not specs, so you can outspeed Regice), make it Rash 4 attacks, and revenge kill everything. In fact, it can also counter Regice by surviving Iron Head with Sturdy, outspeeding with the Scarf, and doing this in return:
252+ SpA Carbink Power Gem vs. 156 HP / 0 SpD Regice: 554-654 (162.9 - 192.3%) -- guaranteed OHKO
Which more than likely means your opponent will switch out to something that can take the Power Gem, and you should go for Earth Power or Moonblast instead. There is a problem here though: You still can't outspeed fully-invested Mega Aggron and Mega Steelix! 230 base speed is simply beyond Carbink's ability to beat without both Scarf and a +Speed nature, which drastically reduces its nuking power. So to be honest, your best bet is to not even try because really, who would run fully-invested base 230?
The Carbink mini-nuke set I've come up with looks something like this:
GRENADE! (Carbink) w/ Choice Scarf
Ability: Sturdy
EVs: 104 Atk / 252 SpA / 152 Spe
Rash Nature
- Power Gem
- Moonblast
- Earth Power
- Explosion
Feel free to sub Explosion for any sort of powerful coverage option you may have available, such as Psychic or Stone Miss. With this spread, you outspeed max EV'd, neutral-natured Base 230s thanks to your scarf. Remaining EVs go into Attack for you to Explode on things because you're not gonna live more than 2 hits with base 50 defences anyway.
And that's everything of potential interest that I have to say at the moment.
Edit: More things!
People seem to like to advocate the use of Vacuum Wave Primeape to deal with Regice. But actually, Primeape is outclassed by Gallade.
(note: Bold marks the high stat swap-in, italics marks the low stat swap-in.)
Primeape stats: 65/60/105/105/70/95.
Gallade stats: 68/65/125/125/115/80.
Gallade hits harder with Vacuum Wave and is bulkier, and also gets Calm Mind (an actual useful boosting move!), Psychic, Psyshock, Shadow Ball, Signal Beam, Draining Kiss (self-healing!), Dazzling Gleam, Thunderbolt, Icy Wind, and Stored Power, along with an extensive support movepool. Overall, his Special movepool is simply far superior to that of Primeape, whose coverage options are basically Thunder/Thunderbolt, Overheat, and Hidden Power. You can run Bulky Specs Gallade to be able to switch in to Regice, or use a bulky Calm Mind sweeper Gallade and make sure Regice can't switch into you and deal heavy damage to the opposing team as a whole. Overall, Gallade basically does everything better than Primeape would, with the exception of having a worse speed tier when it's already so low as to be irrelevant. (Well, I suppose Gallade also has a Ghost weakness that Primeape lacks and doesn't resist Dark, but the difference in both bulk and power is great enough to counteract that in almost all circumstances.) And if you want to hit through subs, Gallade has Hyper Voice, while Primeape would have to use the inferior Uproar.
Some other interesting stat changes I've noticed:
Gengar is 130/65/130/60/75/110, but then we already knew that. But taking into account that Megas inherit the base form's HP...
Mega Gengar: 130/170/80/65/95/130.
This guy just became even more Uber. Possibly even too Uber for Ubers! With access to reasonable dual STAB in Poison Jab and Shadow Claw, along with powerful priority in Sucker Punch, self-heals with Drain Punch, Elemental Punch coverage, Knock Off, and even Power-up Punch for boosting if for some reason he needs it, Mega Gengar is ready to wreck the face of Ubers harder than ever. Not to mention he still has Shadow Tag and his crazy support movepool remains intact. And 130/80/95 defences are still nothing to laugh at. Turns out Gengar's physical movepool just might be scarier than his special movepool.
Flareon just became a poor man's pure-Fire Heatran, with 65/60/130/95/110/65 base stats. He does serve a different role than Heatran, though: Flareon can potentially put in work as a cleric. 65 base HP is still really low and is still going to pass weak Wishes regardless, but 65/130/110 defences with Will-O-Wisp or Lava Plume for burns looks pretty darn decent, at least at tanking physical hits that aren't Ground, Water, or Rock. Bottom line: 65/130/110 defences with a pretty decent and rather rare defensive type, Wish, Heal Bell, Roar, Work Up, Curse, Baton Pass, Will-O-Wisp, Lava Plume, Baby-Doll Eyes to nerf physical attackers before they can get a hit on you, and even freakin' Stored Power because why not.
Banette is amusing. Its stats are 64/63/65/83/115/65. But when it Mega Evolves, its stats become 64/75/165/93/83/165. And of course Mega Banette has Prankster, along with Calm Mind and a rather nice Special movepool. In my opinion, a good way to run this thing might be:
CroNette Confirmed (Banette) w/ Banettite
Ability: Frisk
EVs: 252 HP / 4 SpA / 252 SpD
Calm Nature
IVs: 0 Atk
- Rest
- Sleep Talk
- Calm Mind
- Shadow Ball
Prankster Calm Mind, Prankster Rest, Prankster Sleep Talk, Prankster GG.
Also, are we going to make all Formes (not just Megas) share the same base HP as the base Forme, or no?