Time for some noms, which I don't even know if anyone cares at this point:
First, I'd like to propose C- rank, as some mons in C right now are clearly not on the same level as others.
Additions:
Magnezone C- This Pokemon is a combination of small niches. It can be a terrain/weather setter with Teleport/Volt Switch, but a Levitate or Refrigerate set can also catch teams off guard.
Arctozolt C- This is the toughest Pokemon to deal with in Trick Room due to its insane dual STAB and options like Low Kick for Ferro. Beyond that, it's also a decent Surge Surfer users with BoltBeam and even Low Kick for Ferro if needed considering Volt Absorb dropped in usage.
Dracozolt C Ok hear me out, RegenVest Dracozolt is THE TRUTH. It actually checks a fair share number of special mons like Zapdos and Inteleon, in addition to some physical mons like Talonflame. Mixed Adapt has merits as well for a pure walbreaker. Surge Surfer is also a thing I guess.
Celesteela C- What it has over the 2 Steel birds is its offensive presence, with wide coverage on both physical and special side. It can't cover for everything though, but between Flash Fire/ Regen and more offensive abilities like Sheer Force, it can really put in work. Leech Seed can also help it make progress, though inconsistent if your opponent has Magic Guard Chansey.
Venusaur B/B- I have found Regen Venusaur to actually be pretty good and easy to just slap on teams. A switch-in to SFLO Lele, Koko, Bulu and Barraskewda, an acceptable midground against Terrakion, Adapt Zydog and TC Zarude, Venusaur also discourages its supposed answers like Heatran from switching in with Knock Off and Earth Power, on top of its ability to spread poison with Sludge Bomb.
Crobat C- Inconsistent due to low damage and no setup like Talonflame, but it can really make progresses while being a decent form of Speed control. Its unique typing is also good defensively, so I can see this a good alternative to Talonflame, especially if you plan to run Mono Brave Bird.
Metagross C I like Metagross in conjunction with Azelf. Tinted Lens wallbreaks much better than Alakazam. While its Speed is a letdown, it has no actual switch-in unlike Alakazam who can't do much against Jirachi or blob while still getting outsped by Koko and the likes. The defensive utility is a bonus as well. After experimenting with other abilities Tough Claws, I'd say it's a fearsome wallbreaker in general.
Umbreon C It's a more passive Mandibuzz, but pure Dark can be better since Mandibuzz tends to switch into Knock Off often, and it also has mo. No U-turn, Defog and having to resort to WishTect for reliable recovery are big downsides that lower its viability, but Heal Bell and ability to Wishpass somewhat make up for it.
Bewear C Somebody already nommed this for C but I want to back them up and agree Bewear can be hard to deal with. The main sets worth highlighting are Triage and Tough Claws. What differentiates it from being a random Fighting-type is the fact that it has STAB Facade, which means it can use burn to its advantage against the like of Scarf Mew that forces Terrakion out for example. Its natural bulk is also nice to compensate for its poor Speed. It's definitely better in practice than on paper.
Pangoro C- Choice Band Technician is really hard to bear if I'm being honest. Storm Throw dunks on Intimidate/Dauntless, Beat Up covers Mew and Ghost, Gunk Shot is a bit short on KOing Fini but still heavily damages it and might even come with a poison to guarantee it can spam its STAB on its next switch-ins provided that it hits. It's still slow and needs some buildaround for Beat Up to pack a punch, though not too much. Triage should be decent enough still I'd think considering its good overall matchup and ability to damage switch-ins like Azelf.
Snorlax C It seems inferior to blobs, but having actual offensive presence helps it maintain some pressure, especially since being slow does prevent opposing offensive foes from coming in freely. Between spreading paralysis with Body Slam or poison with Gunk Shot and potentially leveraging its position with Power Up Punch, it has enough tools to prevent double Regen or Intimidate to endlessly pivoting. Seed Bomb or Heat Crash can also nail Swampert and Ferrothorn.
Tyrantrum C- A very niche wallbreaker that's pretty similar to Terrakion with their strong Rock-type STAB, however Magic Guard Tyrantrum, in exchange for being slower and worse offensive dual typing, is more resilient against chip damage and has a stronger Rock STAB, allowing to spam it more often without fearing immunities like Terra. It also has some defensive utility to force out mons like Talonflame and non-Weather Ball Zapdos and if opting for Dragon Dance LO, can even take advantage of Corviknight while still surviving attacks like Grassy Glide from Zarude.
Lanturn C Lanturn does a lot of things Dracozolt does but also has Volt Switch. In this regard, it also competes with Swampert. Both have access to a blockable pivot, though they all can limit them somewhat, with Swampert having a Ground STAB move and potentially Stone Edge for DesoLand users while Lanturn threatens most Ground with Scald and Ice Beam. Lanturn is kinda a midground between Dracozolt and Swampert, it's harder to get cheesed by Hurricane confusion, can spread Para with Discharge and check stuffs like Mence and Talonflame better, in exchange for matchups against Ground-types and inability to block Volt Switch.
Avalugg C/C- Ice-type is obviously what holds it back the most, but its physical bulk is enough to offset some of it. Dauntless Shield is the most common ability to augment its bulk but Refrigerate can be a cool option to have an unblockable Spin. Flash Fire, Scrappy and Magic Guard are other niche options but they all have their merits.
Glastrier C+ Glastrier is severely underexplored and underrated. We have seen others yield successful results with it, with Isaiah having an interesting Sticky Hold application on stall for a reliable late game wincon that also prevents Trick from disrupting defensive backbone. Then we had DeepFriedMagikarp with Water Absorb that is a massive pain thanks to its natural bulk letting it Sub almost effortlessly against passive walls. Personally I also had successes with Regen as well. It can eat some hits you really don't expect like DesoTran's Magma Storm or Zarude's CC all while preventing pivot from easily getting breakers in due to its low Speed.
Vikavolt C+ Imo the best Web setter if you don't go full HO, in which case Ribombee is preferred. However, I find Web to be very hard to keep on the field if your Web mon just dies, especially when you have to commit to slower teammates to make full use of it. Flash Fire Corviknight can easily clear Rock against Azelf and other Fire mons that you use to control Barraskewda, and Flying/Boots mon can really screw the Speed tiers, especially if you face Defog Zapdos or Talonflame (Granted, they are rare, but they do exist). As such, Vikavolt's bulk and its natural offense even without investment can set Web pretty consistently even if it does get cleared. Its Electric typing also means it threatens most common Defoggers, unlike Ribombee which just has to sack itself against Corvi or Moltres to guarantee it. Besides that, it can hold loose ends to check Zarude, Talonflame and other mons depending on ability, as well as slow pivot.
Changes:
Terrakion A -> A- Gapdos is favored for a wallbreaker now thanks to Brave Bird's higher damage and Stone Miss being unreliable.
Barraskewda A -> A+ This thing can be slapped on just about anything related to offense and balance as Speed control and to check stuffs like Volcarona that 6-0s more teams than it should. Despite its basically nonexistent bulk, it can still switch into Fire types like Heatran so never deadweight in any matchup.
Talonflame A -> A- Sorry UT, but this thing has consistently failed to OHKO stuffs it should, like it can't even OHKO Vikavolt with Flare Blitz. With Koko and Skewda being more common, on top of the fact it barely outdamages Swampert and Chomper's Regen makes this really bad at forcing progress against anything other than Toxapex, which can still outlast it if it has Knock Off.
Mandibuzz A -> A- I think everyone can agree towards the end of gen 8 how detrimental Mandibuzz's Rock weakness can be, especially in situations it has to take Knock Off or Trick/Switcheroo. It's a great mon still, but it's tricky to clear hazards with it sometimes.
Cinderace A- -> A Cinderace has been a pillar for offense teams after Super Fang got traction. It means Fire immunities like Corviknight and Zapdos can be kept low when coupled with Taunt. And its other moves like Court Change, U-turn still provide immense value for offense, notably the former to discourage hazards just with its existence.
Landorus-T A- -> A RegenVest Landorus-T only became more and more popular, and for a good reason. It has all the utility attacks in the world, and its typing + special bulk is just enough to fill that RegenVest role well. Offensive lead is a thing that's kind of overlooked as well, since no Bounce means getting Rock + 1 for 1 becomes that much easier.
Moltres B+ -> B Being immune to Water/Ground is nice with DesoLand until you realize Swampert can pack a Rock move or Toxic. Volt Absorb SpDef has some value in dealing with Koko and SF Lele but it still loses to Pixi Koko with Taunt and also relies on Boots, meaning it can't even stay in against full health Ferrothorn.
Chandelure B -> B+ Chandelure feels pretty easy to slap on offense, though it struggles compared to Cinderace primarily due to its Speed. However, hardwalling Barra as it switches in is neat, as is its capability to dunk on blobs with SubCM. Ghost also gives it a Fighting immunity and all the defensive value so worthy of a rise.
Moltres-G B -> B-/C+ The only thing this is good for is fishing for hax with flinch/confusion but otherwise taking 2 turns to set up and still having meh damage is too painful. It does have defensive role on offense but other than that it's not worth trying to make it work.
Togekiss B -> B-/C+ Tapu Lele is better than Togekiss most of the time, especially with Psyshock to damage blobs, the better defensive utility isn't really enough.
Volcanion B -> B+ Mixed Volcanion is such a self sufficient breaker that I think warrants a rise. It is immune to passive chip damage while also not easy to deal with via Regen scouting. It can also spread status and has respectable defensive utility. Desolate Land can also tech Heat Crash for blobs which is pretty neat.
Volcarona B -> B+ I swear this just 6-0s so often that it warrants a rise. It also provides a switch-in to SF Lele with small investment and Barra if DesoLand.
Doublade B- -> B Having a switch-in to Gapdos and Terrakion alongside some other Pokemon depending on EVs makes this pretty flexible, to me at least. It also deals respectable damage, especially with Swords Dance, enough to not just let foes cycle Regen while discouraging foes like Zarude from just getting in due to its coverage. Again, being slow is great to just prevent opposing pivot from going to their breaker.
Entei B- -> C+ This just doesn't feel good to use or stick on a team. DesoLand feels worse than Cinderace without U-turn to get out of PSea and is weaker although it comes with high burn chance. Ate is just meh and only decent if it's paired with another Fire with DesoLand.
Cobalion, Conkeldurr, Darmanitan-G, Diancie, Milotic, Pikachu, Porygon2, Raikou, Zamazenta-C, Stakataka C -> C- These should not be in the same tier as others in C. Cobalion is just bad, weak, and hard to fit without Weavile. Conkeldurr, Porygon2 and Stakataka are hurt by Magic Bounce ban nerfing Trick Room, and Conkeldurr is not even better at Triage than Pangoro or Bulu. Darm-G is a pure mu fish, and not even a good one. Diancie is really hard to justify taking a Regen slot when many mons it's supposed to check like Zapdos and Heatran can get around it. Milotic's higher SpD is not enough to justify over Blastoise who has Spin and EQ to punish DesoLand. Pikachu, like, who even uses it? Absolutely 0 defensive utility. Raikou has Scald, sure, but you'd rather use Xurkitree which already has tools to get past Garchomp and Swampert while Raikou just doesn't even do much to Swampert, much less blobs. Zamazenta-C in theory is ok, but really it turns into Rest bot way too often.
Will edit in replays later, too many old accounts and games to post them all now.
from B+ to A-
from A to A-
from A+ to S
from A to A+
from A- to A
from B+ to A-
from B+ to A-
from B+ to A-
to A- - I think it just struggles a bit too much with Gapdos as people's go-to fighting. Still strong, just not as strong as it was.
to A - Same deal as Ferro. May be a bit less good now that Kommo-o is gone as it was the best Drum check but I still think Pex is great. Has great utility moves in Knock/TSpikes as well as Bounce sets with Infestation being fantastic lures. Again, may fall off a bit but I doubt it will be severe enough to drop it below A.
to A- - Broken fast primsea mon does primsea things
to B+ - Molt is underrated af as a strong Deso mon with role compression as a Fogger/pivot mon with recovery. STAB Weather Ball hits super strong and it is great at getting other broken walls in with U-Turn.
to B - Deso sets have become the wave, just showing how versatile this mon is (and SFLO sets are no slouch either)
to C - fell off
to UR - fell off
to B- - I think Suicune is in a really cool place atm as a bulky Water that is a consistent physical DesoLand check (not weak to U-Turn) that is moderately fast and can threaten with setup. I've been running Regenerator sets with Sub/CM/Scald and then one of Roar/Weather Ball (WBall lets you hit Deso mons for some damage). The set is fairly consistent at spreading status through Scald and pressuring the opponent with spamming Sub/CM and is an underrated defensive Water-type option atm.
to C - Raikou is definitely not vying with Koko as being AAA's premier electric type, but it does have a niche as a fast ESurge mon that fires off powerful Rising Voltages while having Scald to hit ground-types such as Lando-T and Garchomp and threaten burns. Pairing Raikou with Koko gives you a nice Electric spam core where both threaten the others checks (Raikou threatens physdef Ferrothorn w/ Rising Voltage at +1, doing 61-71 while Koko threatens special walls such as Blobs and helps wear down common checks such as Jirachi). It's definitely niche but I think it's solid.
Lmao the most success I’ve had with him is on my electric surge team, that also has Desolate land Heatran and another surge surfer in Xurketree to cover all 3 of those annoying mons 
)
though. Toxic does shit-all to chansey because they have regenerator, soft-boiled and teleport to just laugh at that. Eleki has the benefit of outspeeding barra, koko and even the occasional scarfer. It also has great choices for utility, as explosion to deal huge damage/keep momentum, rapid spin to keep hazards off, espeed and screens to be bad tapu koko. Jolteon has literally none of these in exchange for not beating the blobs and getting chipped down horribly quickly. Not enough of a niche for C-, imo.