I'm fairly new at this, but I figure you guys might appreciate input on the metagame from a newer player's perspective. ^^
As a new player who has binge played on alts constantly, the scariest thing to switch into for me is definitely Specs Scrappy Swellow. It's an offensive powerhouse that requires literally no support to use and it's ready to go. I've used it myself as well and it is monstrous. Steels run the risk of being roasted by Specs Heat Wave, and the only Rock-types in the tier are Gigalith, Tyrantrum, and Rhyperior, which can be hit with U-turn on their entry to swap to a check of your own. Even Goodra as fat as it is has major trouble switching in. Specs Scrappy Exploud is more scary and has practically unwallable coverage, but its lower Speed means that it requires Sticky Web or Tailwind support to be effective (stall just outright loses to Exploud though), whereas Swellow's biggest defensive worry is usually just SR. Logically, this SHOULD cause an increase in specially bulky Rocks and maybe full Sand team builds with maybe a Sand Rush Stoutland or something, but I strangely do not see that even on the mid ladder. I've resorted to pulling mons up from below RU like SS Omastar/Barbaracle to set up on and punish Swellow after it gets a KO, but I seem to be the only one doing that? You can damn near ALWAYS turn out a whole win from a situation that would otherwise be a really hard loss.
Toxicroak walls too much in this meta and the Water-types are getting fed up enough to start using HP Psychic. I saw an Aerial Ace Golisopod today which seems to be engineered for the same purpose (not something I would do but yeah). Apparently Toxicroak is seeing a jump in usage because Gligar used to be here and is now gone, eliminating the need to cram Ice Punch into a moveset, which I understand, and Croak is good enough in its own right to justify the usage anyway. If you're laddering, just know that competent players are literally putting HP Psychic on their Milotic and Vaporeon now. They weren't doing that at all a week ago so this has to be a recent trend. Someone on PS told me about it and I don't remember who, but I didn't really believe it until I started getting hit by it. More Mantine sets are using Air Slash now too (edit: Air Slash is in its RU analysis after I looked, but it seems notably more common to me now that it did a bit ago in which Toxic was what they carried instead, this was likely influenced almost entirely by Toxicroak's presence though too, because it had to have been such a safe and obvious switch until Mantine users wised up).
A lot of people seem to have trouble with Necrozma because it's so versatile in how it can gear up to ruin your life. Pyukumuku is a shitty, one-dimensional mon that will not make you a lot of friends but it is excellent sweeper insurance, especially against Necrozma, which can't use Taunt and probably wouldn't try to fit it into a moveset anyway. You can use a more physically bulky build to better take on stuff like DD Zygarde 10% and Flygon, but I generally prefer a more specially bulky one if I do use it. It's super important to keep in mind the drawbacks of the Unaware ability though, mainly that big moves that lower the user's stats like Draco and Superpower won't see a damage decrease after repeated use against you, so you have to keep that in mind. Also, use Rest for the fourth move if you're afraid of getting beaten by Toxic. A lot of people like using Slowbro to check Necrozma but I feel they're eventually going to start using Signal Beam or maybe SD sets with X-Scissor (maybe even Buginium Z) to get through both Slowbro and the Darks that wall Photon Geyser/Stored Power. That, and I prefer being able to Soak or Toxic the switch in after Necrozma gives up boosting because I'm an asshole. As other people have already noted, Necrozma is becoming more manageable, but it's versatile enough to start "picking its counters" as Necrozma users also adapt. Pyukumuku will just always screw it no matter what.
One huge thing I've noticed is that hazard removal in this meta is actually incredibly easy to maintain because the best spinner (imo) is Mega Blastoise, and Ghosts are too scared to come in on the boosted Dark Pulse. This makes stuff like Specs Swellow that much easier to terrorize the tier with but it also gives a palpable amount of breathing room to stall teams that switch a lot for Regenerator recovery or whatever. Hazards in this tier are not scary unless you run hyper offense and the chip damage is the reason you die in one hit before it's convenient to get your hazard remover out.
Alolan Marowak is really scary if it's healthy and can set SR with its offensive pressure but at least it won't try to spinblock Blastoise. It does fare well against Toxicroak, Salazzle, and unboosted Necrozma, and the no-recoil Flare Blitz is super painful, so its presence is not to be understated in the grand scheme.
Why are people running Slowbro and not Slowking if the reason it's seeing more usage is to check Necrozma? Is it because of Machamp? I don't mean to "promote" the viability of anything out of the tier here but as far as the topic goes, for people who still want that Water/Psychic without being really slow, Bruxish can probably fit the bill as a more offensive alternative, and I've seen it a little but not much. I actually hope it sees more usage because not only can it check Necrozma (at least before it starts running Signal Beam/X-Scissor), but it also fits well in RU with the Dazzling ability because it blocks Sucker Punch (Bruxish outspeeds Honchkrow) and also lets it switch in on Golisopod's First Impression without fear and finish it off. Strong Jaw is obviously offensively better but Psychic Fangs will still OHKO Machamp with Dazzling if Banded, so that's something too.
Other more condensed thoughts on the current meta:
I find Donphan really underwhelming. I shouldn't be able to beat one with BU Toxicroak. It seems people are investing into special bulk or something. Flygon is a bad mon to me, but it's at least more versatile than Zygarde 10%, which I also consider bad and highly predictable, but the Banded Outrage hurts sometimes right before I revenge kill it. Tyrantrum is scary but easy enough to deal with after it kills something. I feel like people regret not having HP Grass on Raikou more than they will admit, but it's otherwise a pretty good sweeper. Hidden Power in general is a nice snub against a nice handful of the top mons here, which leaves a lot of room for surprise attacks that things with 4x weaknesses like Toxicroak and Salazzle should be wary of imo (not just shit like HP Ice for Noivern, there is more to Hidden Power than just Ice and Fire). Trick Room is fun I guess but highly susceptible to hax before getting itself going, not to mention Taunt and Roar/Whirlwind to prevent the move from being used at all. I see more Tsareena than Shaymin and I find that very strange considering that Toxicroak totally walls the former but not the latter, and there are better spinners that don't risk sacrificing momentum a lot of the time to such an abundantly used mon. Drapion is an excellent team glue and good soft check against Necrozma, which is something major it outdoes Toxicroak at, and the fast Taunt is handy as a lead or against stall or balance. I don't know why people use Venusaur when Vileplume exists and gets Strength Sap. Passimian is a great Scarfer with a lot of crowd control and I'm surprised I don't see it more often. Espeon gets knocked around hard in this meta and has to be played very carefully. Florges is overrated to me and creates too many momentum losses due to it typically carrying one attack that makes it very easy to predict and wall, so I actually kind of hate it.
I don't think anything is broken or busted, this game is actually pretty fun. Sorry if this was long-winded or misplaced or anything. Anyway, these are my thoughts.