Rises:

Whiscash
New -> B- Whiscash would have dropped to PU if it didn't rise to RU last month. Hazard control is decent
enough in NU and the tier is pretty hostile to Ground-types with the plethora of immunities and resists that can take advantage of Whiscash.

Muk
A+ => S- A grounded Poison feels almost mandatory for balance structures right now, and Muk is a perfect fit for those styles of teams. Phenomenal special bulk and multiple ways to spread poisons and lots of utility moves like Haze and Zen Headbutt for opposing Poison-types to win the Toxic Spikes war.

Rotom
A+ => S- Rotom has a positive matchup against all other S ranks. It's set diversity makes it incredibly difficult to answer, and because it beats Ground-types, it has a virtually unblockable pivot move to enable other powerful breakers like Zoroark and Bruxish. Bulky Dark-types can shrug off Rotom's hits but still dislike being burned and can become setup fodder to Tera Fairy Nasty Plot sets.

Zoroark
A+ => S- Beyond the mindgames Illusion presents in such a volatile tier, simply identifying Zoroark's set can be a whole other headache in itself. Choice Specs sets shred most of the tier, but reasonable checks like Umbreon and Chansey are super impaired by Knock Off or Trick with a Choice item or just get U-turn'd on. Zoroark also has an amazing speed tier, making it very difficult to check offensively.

Cacturne
A- => A Cacturne is just an absolute menace offensively, with an oddly amazing defensive profile that gives it many opportunities to hit the field. Leaf Storm straight up OHKO's Passimian, and Cacturne's Water immunity and threatening presence lets it set up Swords Dance to break and sweep with Sucker Punch quite easily. With flavor utility moves like Encore, Leech Seed, and Spikes in the mix too, Cacturne finds itself being easy to use and very difficult to deal with.

Haunter
A- => A Similar vein to Cacturne; oddly great defensive profile despite its terrible bulk, which allows it to use its excellent offenses even better. Haunter also has an insane utility movepool with options like Encore, Toxic Spikes, Trick, and Destiny Bond on top of its Nasty Plot + perfect Ghost / Poison / Fighting coverage.

Lurantis
A- => A Lurantis has cemented itself as one of the best and most consistent Defog users in the tier, with a positive matchup against Sandaconda, reliable recovery, and a very dangerous combination of Leaf Storm and Contrary. Lurantis has excellent bulk and only needs one Leaf Storm boost to really start tearing apart the tier.

Appletun
B+ => A- Appletun is a nightmare for defensive teams to switch into with hazards up; Apple Acid and Leech Seed mean you can't just sit in front of it and Dragon Tail keeps shuffling teams. Appletun's bulk is also excellent and with Tera Steel to invert its Ice weakness and grant a Poison immunity, it can be super difficult to take Appletun out, much less take it out without taking significant damage from it.

Glaceon
C -> B- Glaceon has risen in usage due to its great bulk and power, access to Calm Mind and Freeze Dry, and insane offensive coverage with Ground Tera Blast.
Drops:

Vaporeon
S- => A+ With increased usage in Toxicroak, and a meta currently dominated by Electric- and Grass-types, Vaporeon struggles to make use of its bulk, as amazing as it may be. Many setup sweepers like Dudunsparce and Muk can soften Vaporeon up and drain its PP even if they can't consistently setup due to Haze. Offensive sets making use of Calm Mind, Tera Blast, or Ice Beam have seen use lately but it's not enough to set Vaporeon apart currently.

Drifblim
A+ => A Drifblim's amazing bulk and Defog makes it a great pick for defensive teams, but as the meta has developed, its passivity has become incredibly exposed. Drifblim's reliance on Strength Sap makes it very easy to just send in weak and deny large pools of HP. Powerful special breakers like Clawitzer and Zoroark get relatively free entry on Drifblim due to its weak uninvested STAB moves and threaten easy OHKO's or free pivoting. Hazard control also isn't as valuable anymore with Pokemon like Lurantis and Oricorio-F seeing more usage to fill these roles.

Qwilfish
A+ A+ => A Qwilfish is an amazing bundle of perfect utility, but is hampered by its mediocre stats and lack of recovery. With hazard control being stronger, Spikes are slightly less potent as they once were, and people now know to not just keep Toxic-prone Pokemon in against Qwilfish, and there are many Toxic absorbers like Ursaring, Sandaconda, and Tera Steel / Poison Pokemon ready to smoke Qwilfish at a moments notice.

Chansey
A => A- Being reliant on Seismic Toss and status makes Chansey very passive and easy to take advantage of, especially with the possibility of Tera Ghost and Substitute, anything can potentially wall Chansey.

Mabosstiff
A => A- Without Stakeout this thing hits like a wet napkin.

Perrserker
A- => B+ Poor bulk for a "Steel-type", still a solid pivot but bad matchups into all the S ranks and super vulnerable to status..

Camerupt
B => C+ Terrible bulk only barely saved by an amazing typing, super passive even with threatening burns or Yawn.

Rotom-Fan
B => B- Outclassed by regular Rotom with a worse typing and not much to gain from it (Air Slash)

Sawsbuck
B => B- Relies purely on Headbutt flinches, vulnerable to all hazards and status, pretty much all contact moves with low BP and has poor bulk.

Vespiquen
B => B- Pretty Tera reliant for a defensive Pokemon, Spikes aren't as insane with all the removal options we have.

Zangoose
B => B- Many Pokemon can match Zangoose's power without being on a timer.

Basculin
B- => C+ Better Water-type breakers like Bruxish and Clawitzer.

Charizard
B- => C+ No Roost really hurts Charizard, but there's really just stronger Pokemon that can also match the speed tier.

Crocalor
B- => C+ Needs Eviolite and weak to Stealth Rocks, makes a lot of would-be 3HKO's into 2HKO's

Dachsbun
B- => C Super passive and vulnerable to status and hazards, Fire immunity is neat but doesn't provide much for the tier.

Honchkrow
B- => C Reliant on Brave Bird because Sucker Punch and Night Slash are weak. Needs Heavy-Duty Boots or it becomes very squishy and easy to pick off.

Skuntank
B- => C+ Great utility and typing, but super passive and lacks recovery while having only average bulk.

Spiritomb
B- => C+ Bulk is not as good as it appears, and is very passive without multiple boosts.

Masquerain
C => UR Webs suck.

Oricorio-P
C => UR No reason to use this over other Quiver Dance users.

Quaxwell
C => UR Rapid Spin is less valuable with all the hazard control options available, so it's not worth using a literal sitting duck.