Alright here's my quick thoughts:
edit: this was in fact not very quick, here are thoughts on
30 Pokemon in our favorite tier.
(warning. beginning noms are controversial and i really just want discussion on them, not necessarily agree with them)
Emboar from S -> A+
Reasoning: Sigh, what goes up must come down. Emboar seems a bit underwhelming and one-dimensional as of late, probably because of its trouble finding a spot as a fire-type when the multi-dimensional pokemon Delphox is so freaking amazing right now. I don't want to say any more on this controversial one that I don't necessarily agree with but mainly want to bring up as a discussion point.
Virizion from A+ -> A
Reasoning: Virizion just really isn't what it used to be in the tier, with lots of defensive flying types in Xatu and Golbat around to metagame adaptions like HP Flying Rotom. Psychic types like Xatu and Delphox, Fire Types like Emboar and the aforementioned Delphox, and Ice types like Vanilluxe are really taking away from this mon along with there being a superior grass type in Whimsicott. Physical sets have trouble setting up and unboosted attacks have trouble netting important KOs (can't KO bulkier varients of Xatu with Z Stone Edge or Golbat with Z Stone Edge even after rocks, Leaf Blade 3HKOs Slowbro unboosted, garbodor can switch into a close combat and still survive Z Zen Headbutt, etc.). Its special sets have issues with damage output from a weak giga drain and focus blast having its obvious accuracy issues. Yeah it is still good on Grassspam and has very good bulk but its really not A+ level anymore.
Sneasel from A+ -> A
Reasoning: Sneasel also isn't what it used to be, as with the rise of more physically bulky Pokemon like Piloswine and Miltank as well as it being a dark type that loses to Slowbro, which sucks. Vanilluxe outclasses it as an offensive Ice-type and while its arguably the best Pursuit-trapper in the tier it relies on a lot of 50/50s as Pursuit can't take some important KOs without the opponent switching out. Houndoom is on the rise and a very underrated pursuit trapper and Sneasel's defensive typing leaves it really weak to priority in mach punch and bullet punch coming from fighting types that are gaining popularity (particularly Hariyama and Medicham with bullet punch) Whimsicott outspeeds it and Ice shard can't KO it which also sucks; Delphox commonly runs scarf and can use this as an opportunity to either revenge kill or feign a scarf set and setup Calm Mind on the switch. Honestly meta hasn't been kind to Sneasel - Sneasel usually does well vs. frail offense but the meta is getting bulkier especially in the fat waters department with vanilluxe being so prominent.
Guzzlord from A -> A-
Reasoning: Jim has plummeted in use from what I can see, with Mega Audino being everywhere and Dazzling Gleam becoming Standard on Missy and Delphox the meta has adapted to what was the rage before. Vanilluxe is a stronger, faster, and overall superior special attacker that relies a helluva lot less on prediction than guzzlord does in general. Slowbro has dropped a lot in usage as well which hurts Guzzlord's usefulness in the meta.
Samurott from A- -> B+
Reasoning: Yeah its a versatile attacker that can run both physical and special sets but hell its not even NU by usage. its too hard to play around with all these Electric and Grass types running around and it doesn't have very much bulk at all. Special sets are hard to use because of limited coverage. Physical sets have nice options in Megahorn and Superpower but generally it doesn't have very much use in this current meta.
EDIT: I take this nom back
Accelgor from B+ -> A-
Reasoning: I've been playing around with Accelgor lately and I really find it nice - with Choice Specs it makes it an incredibly powerful cleaner because of its amazing speed that it can reach unboosted. It gets Sludge Bomb to hit annoying Fairy types that resist its STAB and Focus Blast to hit Steel types that resist Bug Buzz as well. It has access to Spikes which it can run on offensive and fast lead sets and Final Gambit can be used to block spin and defog reliably as it is faster than any unboosted hazard removal in the tier.
EDIT: I take this nom back
Cryogonal from B+ -> A-
Reasoning: Im going to echo some sentiments here from others and myself: Cryogonal is one of the most consistent spinners due to it's reliable recovery, awesome special bulk, and great offensive typing. Access to Freeze Dry lets it nail Seismatoad and Omastar while still hitting the normal things Ice can hit. Immunity to Webs, Toxic Spikes, and Spikes make up for its rock weakness along with soft checking Vanilluxe and other special attackers in the tier.
Klinklang from B+ -> A-
Reasoning: Klinklang has really evolved from the Z Wild Charge sets that used to be really common when people tried to use it. This thing is able to set up on commonly used Pokemon such as Whimsicott, Xatu, Ice Cream, and Garbodor. Slowbro is on the decline, leaving very little Pokemon that are able to stop a boosted Klinklang in the sweep. Its synergy with Xatu is also really really awesome as previously stated by somebody, as all the Stealth Rock users that beat Klinklang lose to Xatu while Piloswine, Steelix and Rhydon, get set up on by Magnet Rise Klinklang.
Sir Kay introduced me to another great Klinklang partner in Lurantis in which I will get more into later in this post.
Malamar from B+ -> B
Reasoning: Malamar has been really underwhelming lately in my opinion, Fighting coverage really hasn't been that useful lately. What really kills this for me is how easy its able to get momentum - quad fighting resists in Scyther, Golbat, and Xatu that are popular or rising
all can switch into Superpower an U-turn out to a knock off absorber that can finish Malamar off or just flat out KO'ing it, capitalizing on Malamar's 4x bug weakness. Z-Happy Hour has its use and is a cool set, but is hard to fit on teams. Happy Hour also has to forgo the more reliable RestTalk set from the previous generation. Malamar doesn't have the speed to sweep/clean and needs setup to wallbreak, making it easy to switch to a check or counter. Once it gets going its really good but it still struggles to find opportunity despite its amazing ability Contrary.
Hariyama from B -> B+
Reasoning: Hariyama is really cool right now, having two great abilities (well three but 2 relevant great abilities), in Thick Fat and Guts. While its not the level of Machamp power wise with Guts, its pretty much very similar in many ways to the powerhouse that left NU some time ago. Priority in Bullet Punch and Fake Out along with STAB Close Combat make Hariyama really potent in the current meta. Thick Fat makes Hariyama an excellent specially defensive wall, checking the likes of Houndoom and Vanilluxe as well as others. Its main drawback with this set is that it wishes it could beat Delphox but it really cannot.
Liligant from B -> B-
Reasoning: Mono Grass coverage kinda sucks despite having Quiver Dance; Z hyper beam is its redeeming feature but thats just a one time use with mere neutral coverage at best. Sleep Powder has accuracy issues while Vivillon has Compound Eyes to deal with that. The common Scarf Delphox can flat out switch into anything besides Z Hyper Beam as it can outspeed Liligant with a Choice Scarf. Vivilion just outclasses it to an incredible degree.
Miltank from B -> B+
Reasoning: Miltank is just an awesome support mon that can also check ice types like Vanilluxe. It gets rocks but it also gets recovery in Milk Drink and Heal Bell which is what sets it apart from Piloswine which also sets rocks while checking Vanilluxe.
Medicham from B -> B+
Reasoning: Medicham's Pure Power is really amazing and it can run a variety of sets from Choice Scarf to Life Orb to Choice Band to some random coverage Z move. Its access to elemental punches lets it have versatility and unpredictability and can catch an opponent off guard. Choice Scarf particularly makes a great cleaner on top of high powered STAB moves like High Jump Kick. Life Orb can run Fake Out and Bullet Punch which do a ton of damage before a fast and frail opponent can even make a move.
Raticate-A from B -> B-
Reasoning: I think A-rat is kinda bad right now as its outclassed by Sneasel and Houndoom in the pursuit trap category and it has accuracy issues with Hustle. Its a decent Breaker and Swords Dance with STAB sucker punch is really cool but thats not enough to let it stay in B in my opinion. Thick Fat is nonexistant on Alolan-Raticate as far as I know. Meeps would be disappointed in this I know.
Typhlosion from B -> B+
Reasoning: Typhlosion's Specs-boosted Eruption is one of the hardest hitting attacks in the tier, 2HKOing normal fire resists such as Miltank or Seismitoad after rocks. Its also faster than you probably think it is - it can reach a pretty great 328 speed with a Timid nature, letting it outspeed many of the non scarfed Pokemon in the meta. When you take something with suck power and give it good speed you're bound to have a mon higher than B here.
Aurorus from B- -> C+
Reasoning:
Completely outclassed by Vanilluxe, I don't even know whats going on here especially since Veil has been banned. Yeah it sets rocks but there are tons of mons that set hazards more reliably than Aurorus can. It has one niche in a bulkier Hail setter that can set rocks as you can see by Z+V's hail team which is pretty good, but I can't see many options for it now.
Sawk from B- -> B
Reasoning: This thing is POWERFUL. Choice Band Sawk makes an excellent wallbreaker, and while sporting an average speed tier its great attack on top of STAB Close Combat make it one of the hardest hitting Pokemon in the tier. This OHKOs many things that it hits neutrally, and 2hkos many resists - Adamant Banded Sawk has a favorable chance of OHKOing Delphox after Stealth Rock. Sturdy is an incredible useful ability on a Pokemon like this, so if hazards stay off the field than Sawk can almost always get a guarenteed KO or two somewhere throughout the match. Knock Off allows it to hit Ghost and Psychics harder, Poison Jab lets it hit Fairy-types, and Stone Edge lets it hit Golbat and Xatu. Scarf Sawk makes an excellent revenge killer that often has two chances to break a pokemon due to Sturdy. Mold Breaker can even be used on Adamant Band to have a high chance to OHKO Steelix with the nuclear STAB Close Combat.
Uxie from B- -> C+/C
Reasoning: Slow, weak, and unreliable, Uxie's only real use is for Trick Room or Memento support.
Regirock from B- -> C/C-
Reasoning: Why is this so high? Its not even close to one of the best rock setters out there and the only way I'd ever use this is to be a sun setter on a sun team. I dont like this Pokemon at all and its weak, its redeeming factor is that it can threaten Xatu but thats not B level material here.
Aromatisse from C+ -> C-/UR
Reasoning: Why is this even used? Its just a worse Mega-Audino without a Ghost-type immunity and worse movepool. Mega Audino has no opportunity cost either as the meta has no other mega evolutions so I find no redeeming traits in this mon.
Jynx from C+ -> B-
Reasoning: Jynx really has some use in this tier because of its power and speed, but also because of Z-moves. Z Lovely Kiss is a decent set that allows Jynx to use its good offensive typing with the speed boost to clean up an opposing team. Z Focus Blast allows it to hit things like Steelix, Incineroar and other Steel and Dark types that normally beat Jynx with ease. Access to Nasty Plot and a very good ability in Dry Skin also add to the usefulness of this Pokemon.
Pyukumuku from C+ -> B-
Reasoning: Pyukumuku is the best setup stopper on stall teams in the tier, and with an amazing support movepool its deserving of B- just based on its crucial role on Stall teams. Great defensive typing leave it weak to only Electric and Grass, making it easy for other pokemon to cover those bases with relative ease.
Type: Null from C -> C+
Reasoning: Earth really summed this up well for me but great wincon with amazing bulk, sets up on things like Delphox, Scarf Vanilluxe, and other special attackers really easily.
Probopass from C -> C+
Reasoning: Great special bulk and Magnet Pull are really useful in this meta. Tons of random shit appreciate Steelix being gone and the ability to set rocks and be a slow pivot with Volt Switch makes this mon worthy of a higher ranking. Magnet Rise helps make up for the bad defensive typing (and is the reason it beats Steelix) but its funny how Delphox always thinks it can 1v1 this thing as I've seen on the ladder recently.
Alolan Persian from C+ -> C/C-
Reasoning: Why don't they give Fur Coat to a Pokemon that has decent defensive typing or some defense stat to begin with? I'm agreeing with Eternally on this one.
Mudsdale from C -> C-/UR
Reasoning: God-awful mon, slow as hell, doesn't do anything you want it to, cool ability but it doesn't belong here.
Eelektross from C- -> UR
Reasoning: May have no weaknesses but mediocre defensive typing, stats and outclassed offensive stats leave no viable place for this Pokemon in this metagame.
Ambipom from C- -> D
Reasoning: I've been echoing this in the NU room for a while now, but this low ladder [strike]meme[/strike] favorite is really bad along with Claydol with its only niche being Technician Fake Out. Cinccino is just the superior fast normal type in the tier,
Poliwrath from C- -> UR
Reasoning: Eternally got this one down as well - Can't really check anything and doesn't function even close to the level of other water types in the tier.
Lurantis from C-- -> C+
Reasoning: Super adamant about this one. Kay introduced me to this amazing Pokemon last week when building for Klinklang - it destroys water types, gets recovery, defog, powerful STAB which sets up, and more team support in Aromatherapy. Meadow Plate Leaf Storm OHKOs Piloswine by the way. It destroys potential switch ins with contrary boosting its special attack every Leaf Storm, and being able to crush ground and water types is something really appreciated in the metagame right now. Its a bit on the slow side but the fact that it provides so much support while being an offensive threat means its deserving of a higher rank than the bottom of the barrel.