Hi everyone. I've done plenty of playtesting and even though the metagame is ridiculously centralized, I'm enjoying it so far! The change of landscape from Yveltal + Necrozma-DM + Eternatus to this is genuinely refreshing. Here's a summary of my thoughts:
Eternamax
Eternamax is obviously the elephant in the metagame; its presence is literally and figuratively vast. Having at least two in each team is mandatory: one with overflowing Defense and the other with overflowing Special Defense. The best set is probably Dragon Tail / Toxic / Flamethrower / Recover, but some other moves like Substitute (blocks OHKO spam) and Screech (PP fodder) have some purpose too. In my experience though, the moves don't even matter too much: two Eternamax can pretty easily PP stall entire unprepared teams by just switching into one another infinitely. The choice of items is a little less brainless although still pretty straightforward. Black Sludge cancels out any damage done on the overflowed side, Heavy-Duty Boots shields you from entry hazards, Shed Shell proofs you against Gothitelle and Perish Song + Whirlpool, and Rocky Helmet chips down anyone that's still running physical attackers for whatever reason.
Eternamax pretty much invalidates the overmajority of traditional wincons. Offensive Pokemon that can only hit on the physical or special side (so 99% of previously viable options) are unviable, period. As a result, the metagame is centralized around winconditions that cán beat Eternamax. I'll discuss these options here. Beyond that, 99% of the previous defensive staples are unviable as well, with the Eternamax duo walling all that needs to be walled already. Nonetheless, a few Pokemon have still been able to carve out a niche for themselves, which I'll discuss as well.
Entry Hazards and their effects
With Defog being an unviable move due to every team packing multiple unkillable Pressure walls, Spikes is incredibly powerful and probably the strongest playstyle there is. The rate of progress you can make in this very bulky metagame is catalyzed significantly with three layers of Spikes on the opponents field. The best setters are by far Skarmory and Mew due to their unique traits. Skarmory is immune to OHKO moves, is able to fit Stealth Rock on top of Spikes, and can force progress with Whirlwind. On the other side, Mew has access to pretty much every move in the game, including useful ones like Horn Drill, Fissure, Knock Off, Heal Bell, Whirlwind, Recycle, and Stealth Rock. Apart from Spikes (Stealth Rock if you run Spikes Skarmory) and Rest or Soft-Boiled + Heal Bell, you can easily customize Mew to your needs, which makes it very splashable. The best sets in my experience are Stealth Rock - Spikes - Roost - Whirlwind with Shed Shell for Skarmory and Horn Drill / Fissure - Recycle - Spikes / Stealth Rock - Rest with a Leppa Berry for Mew. Ferrothorn is a fine Spikes setter too, but easier to wear down than Skarmory and Mew.
As discussed, Mew and Skarmory are the most convenient Stealth Rock setters, but others like Fissure Groudon and Knock Off Necrozma-DM work fine too.
Heavy-Duty Boots
With entry hazards being broken, Heavy-Duty Boots are too. Pretty much any Pokemon will benefit significantly from Heavy-Duty Boots, whether it be Eternamax, OHKO spammers, or entry hazard setters.
Knock Off
With Heavy-Duty Boots being broken, Knock Off is too. Sadly, there aren't a lot of viable Knock Off users. Some that stand out are Mew, Necrozma-DM, Cryogonal, and Ferrothorn.
With entry hazards being broken and Defog being unviable, Rapid Spin is pretty luxurious. Cryogonal is by far the best Rapid Spin user. It's immune to Spikes, Sheer Cold, and Fissure, and has access to valuable moves in Sheer Cold and Knock Off itself. Excadrill is another niche option that also has access to Fissure and Horn Drill, but can be worn down relatively quickly.
OHKO moves are the easiest and fastest ways to make progress in the metagame. Some notable abusers are Mew, Lapras, Kyogre, and Groudon. All four can sit in front of Eternamax and fire off repeated OHKO moves. On top of that, Mew can set entry hazards, Groudon can set Stealth Rock, and Kyogre can easily break through the premier Sturdy Pokemon in Skarmory. The Kyurem forms and Excadrill are notable too due to their ability to ignore Sturdy, but they can't switch into Eternamax reliably.
These are some of the very few offensive options that can still put in work in the current metagame. Calyrex-Shadow is still broken; with careful play, it can break past the Eternamax duo between Nasty Plot-boosted Psyshock and Psychic / Astral Barrage / Max Mindstorm, and easily spirals out of control afterwards with As One boosts. Xerneas uses Eternamax as setup bait; it can't be poisoned courtesy of Substitute and is immune to Dragon Tail. After setting up multiple Geomancy boosts, Xerneas can then threaten the Eternamax duo with Moonblast / Max Starfall and Psyshock. Necrozma-DM is immune to Toxic, can negate Dragon Tail with Substitute, and set up to its heart's content with Calm Mind. It can then beat the Eternamax duo with Psyshock and Stored Power / Earth Power. Hatterene ignores Toxic and Dragon Tail with Magic Bounce and its Fairy-typing. It uses Eternamax as setup bait and defeats the duo with Psyshock and Stored Power / Moonblast.
Generally speaking, the key to break past Eternamax is access to Psyshock + a super-effective special move + a setup move + ways to combat Toxic and Dragon Tail.
Some Other Wincons
This is pretty straight-forward; Salazzle outstalls Eternamax pretty easily with Corrosion-enhanced Toxic + Substitute + Protect (+ Disable if you want).
These are probably the best trappers out there. Substitute Gothitelle outstalls Eternatus with Rest + Cosmic Power + Taunt and Azumarill removes Eternamax with Whirlpool + Perish Song, being immune to Dragon Tail as a Fairy-type. Even though its special bulk is worse, Azumarill is better than Primarina because Thick Fat cuts down Flamethrower damage. A lot of other Pokemon have access to a trapping move + Perish Song, but Azumarill and Primarina are the only options immune to Dragon Tail.
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In terms of viability, Eternamax and Calyrex-Shadow are easily the best Pokemon in the metagame. Hypothetically speaking, Eternamax would definitely be S+ and Calyrex-Shadow would be S. The A-ranks would consist of Mew, Skarmory, Lapras, Gothitelle, and Yveltal (maybe Hatterene too because Magic Bounce is awesome). Everything else would come afterwards.
That's all, ciao!
