I'm gonna go on and add to the already existing plethora of noms being made since there are a few things I think should be acknowledge that haven't been so far. Hope you enjoy reading!
Also thanks to Shitbat for stealing half my noms
Swampert down to A-
This one may be a little more controversial, though I feel that Swampert struggles to act as an Electric-type check as reliably with Rotom-W in the tier. While sure, it can still reliably set rocks or get a Toxic off on Washtom, it's sustaining major damage in the process and keeping itself from possibly setting up rocks another time in the match, which can be a big problem. I also think that Swampert struggles for a teamslot more than before with Gliscor and Seismitoad, the latter of which particularly gives it tough competition due to its ability to counter Rotom-W, proving themselves to be very worthwhile Ground-type rockers as of late. It can also struggle to check things like Infernape and Nihilego as easily as Gliscor or Hippowdon due to its 4x Grass weakness and lack of recovery, the latter of which can be particularly troublesome in a meta filled to the brim with chip damage. Overall, I just don't think Swampert has as much of a presence in the tier and in teambuilding as things like Infernape, Mega Altaria, and Mamoswine, and that while still good, a few metagame trends like Rotom-W's dominance and chip damage galore work against it.
Alolan Muk up to B+
Even though I got sniped on this, I'd still like to touch on AloMuk since I think it's one of the more urgent rises at the moment. Its biggest strength is quite obviously its ability to take on Mega Latias more easily than nearly anything else in the metagame, though I've also been finding that it does wonders on VoltTurn as a way of pressuring typical Electric-type resists, most notably the aforementioned Mega Latias, its base forme, Hydreigon lacking Earth Power, Manectric, and Amoonguss. It's just really good at tanking hits from and pressuring the tier's absolute best special attackers, and this in tandem with being easier to fit on teams than earlier on in the meta is absolutely why I can get behind a rise. Krookodile falling off as recent shifts have occurred has also been a bit of a boon, since one of this guy's biggest checks and competitors for a Pursuit trapper is no longer as prevalent or good at its role.
Nihilego up to B+
I was indifferent on this literally like two hours ago, but after talking some with various vr council members, I definitely think that Nihi has more worth in this tier than anything else currently residing in B outside of Alolan Muk. It's an extremely reliable Stealth Rock setter due to its ability to force switches pretty easily, though outside of Stealth Rock it can viably run plenty of extremely threatening sets, including Specs/Life Orb (with some EVs taken from SpA and put into SpD in order to boost Speed upon netting KOs), Substitute, Scarf, and Electrium Z, which is particularly popular among most people that I've spoken to about Nihilego. I generally think that while not a lot has necessarily changed for it, Nihilego just has so much versatility and viability between a lot of different sets that it's hard to compare it to one-dimensional and less consistent Pokemon like Azelf, Blissey, and Volcanion. Super solid mon that really just needs a more accurate rank.
Hippowdon up to A-
Another nomination that's already been addressed, though I feel like this one has gotten a little lost in conversation these last couple posts and that there are some more things we can cover with Hippowdon. Losing to Rotom-W is definitely a huge drawback that comes with using Hippo, but I personally think that in a metagame comprised of teams that look to chip opponents to death with pivoting and hazards, Hippowdon stands as a really solid attack sponger. In addition to handling all of the chip damage better than bulky Ground-types like Swampert and Mega Steelix (largely due to its access to recovery), Hippo acts as one of the most reliable Mega Manectric checks available by virtue of literally not caring about any Hidden Power coverage it could run. It also matches up well against Pokemon that are currently very good/prevalent, including Infernape, Cobalion, Mega Beedrill, and the rising Alolan Muk. Overall, Hippowdon is just a really good answer to a lot of the teams we commonly see begin used in the metagame, and has as much worth of a defensive Pokemon as Amoonguss in my eyes, which should be justified with a rise.
Chesnaught and Florges both down to C/C-
Chesnaught really struggles in the current metagame, given the dominance of Mega Latias and Mega Altaria, which find nothing but opportunities to set up against it. It is also hurt by the prevalence of offensive mons like Mega Beedrill, CB Scizor, Infernape, Alolan Muk, and Primarina. To make matters worse, Krookodile and Crawdaunt aren't as necessary of Pokemon to check given that they've fallen off recently, and Klefki is almost always better as a defensive spiker due to its better splashability, more impressive defensive capabilities, and mucher higher unpredictability. It's just a really hard mon to use right now, and doesn't even reliably check Rotom-W given that it commonly runs at least one of Toxic, Will-O-Wisp, and HP Fire. As for Florges, it just lacks the usage to be able to prove its worth in the metagame and is generally outdone in its role by Sylveon, which has some important advantages over it in the forms of higher physical bulk and a better offensive presence. Both of these Pokemon are just too unused and too hard to actually make work in comparison to similar Pokemon, and I think that drops are warranted at this stage.
Xatu up to C/C+
While Xatu doesn't appreciate matching up poorly against the tier's ever-present Electric-types, it absolutely loves the fact that Weavile is now banned. With Weavile's departure, major annoyances like Klefki and Amoonguss being better than they've ever been, and defensive rockers like Swampert, Hippo, Mega Aggron, and Gliscor all frequently finding themselves on teams, Xatu is quite capable of ruining your day. Absolutely invalidating Klefki is just magical, and doing that in addition to taking on just about any rocker or status spreader the tier has to offer outside of Rotom-W is something that gives it a more relevant and appreciated niche than anything else currently residing in C- (aside from maybe Moltres). I definitely think Xatu can rise right now, since C- felt almost preliminary given that Weavile was still around when it was first ranked.
Hope you guys enjoyed reading! Let me know what you all think, and let's be sure to keep the good discussion going these next couple of days before the update :) I'll be in charge of it this week since Pif is rather busy, so expect another post in the coming days. Thanks for reading!