S

Absurd speed tier, pivoting capabilities, hard to account for sets. Most offense in SS is patched together with duct tape to deal with this thing. Its' vastly above curve with the rest of the dex and every single team you build should have preferably multiple outs in case it starts spamming Shadow Ball.

King of Kills. Its' very easy to overprep Dragapult and be weak to Weavile and it is likewise easy to overprep for Weavile and then lose to Dragapult. Very little actually wants to switch into a well played Weavile and the few things that do often hate the item removal on top of it. A league of its' own.

This might be the one I have to argue extensively for, but here goes;
Tornadus Therians turn one knock off is the single hardest thing to punish in SS OU. Bar none. People complain about "unpunishable interactions" in SS and this is the one I often sit down and ponder as my example of it. Seeing Zapdoses, Landoruses and even Clefables depending on lineup switch on it turn one is ridiculous. Killing the fucking thing turn one is often out of the question and a large reason why Weavile slots Triple Axel comes down to the fact that Icicle Crash, even while Adamant, negatively rolls to kill.
252+ Atk Weavile Icicle Crash vs. 252 HP / 88 Def Tornadus-Therian: 312-368 (86.1 - 101.6%) -- 12.5% chance to OHKO
Ridiculously safe, ridiculously hard to punish are words I use for Tornadus Therian. It's my argued S tier at the moment.
A+

Queen Utility. I don't have much to say on Clefable that others are likely to say; She does a lot and a lot of it is good. Twave Knock Off is annoying, the sparse wish passer is great for making otherwise "frail" mons like Heatran stick around for longer, Calm Mind Unaware keeps most stall teams together, Sticky Barb + Trick is hard to navigate around. Excellent mon.

I've done the "bold" decision to move Landorus Therian down from S tier in my tier list but it mostly comes down to how I perceive Landoruses active impact on any given game. It sticks around, acts as the mandatory ground type and it does that well. But it dosen't feel like an oppressive game piece more than a means in the builder to solve a conundrum. The SS meme of "Landorus T + 5 shitmons = good team" is very much true still, that I will concur.

Spikes and Knock off on top of an incredible typing with a defensive-offensive utility movepool most mons would dream of having. Ferrothorn is excellent.

The standardized obligatory steel type for Offense at the moment. Hits like a freight train, nails status constantly throughout a match and is very hard to switch into. Absorbing Future Sight is also excellent and can save many-a offenses mid games. Great mon.

Bulky Offense and Stall annihilator. Might be the best stealth rock setter in the whole tier and acting as a psychic resist is invaluable. If hazards are off the field this thing can take bad trades and heal up extensively over time. Toxapex having to slot Shed Shell more and more is a sign of how dominant Heatrans presence can be. The Air Balloon Heatran walling the occasional specially defensive Garchomp lineup is also funny. Good mon.

The "fuck you" to the aforementioned fire toad. Offensive SD is incredibly intimidating and without careful preamble can sweep teams on a dime. Specially defensive sets with Toxic are good and come in handy a lot of the time since it lets you slot a lot more aggressive steel types. Solid mon.

I don't build too much with Gking in mind but I can't deny its excellent synergy with Weavile. Some people make it extensively clear how infuriating this thing is as a defensive-offensive Future Sight setter and I can't deny how scary it can be depending on what it is paired with. Trick + Black Sludge + Nasty Plot teams are also terrifying but require a decent bit of effort to pop off. Incredibly consistent mon.

The blue collar worker of birds. Zapdos with static can save your ass way more than you have any right to, sure, but its' the fact that its' on top of being an excellent mon that has one of the best check lists in the whole Dex. It dumpstering a lot of Regenerator cores is also handy. I think defensive Defog sets at the moment are pretty bad and should only be used if you legitimately can't fit it anywhere else but it does the job well enough should you need it. Incredibly, incredibly consistent mon.

The Spine Splitter. Future Sight + Urshifu is fucking ridiculous to pilot comfortably into and it might be the best way to force something to die in the whole dex. Taunt + Pads is good and abuses players that try too hard to contact-punish as their Shifu outplay but Band is by and large the best set. Danger, danger, danger the mon.

Bird Killer. Putting Koko this high up might be surprising but as far as ensuring damage sticks HDB + Toxic Koko is actually sort of cracked as role compression. Resetting Terrain is good, U-Turn + Thunderbolt is a great pivoting tool (even if I dislike the set personally), Calm Mind + Roost can hard-call a loss for Slowbro + Torn T teams. Being faster than Weavile also helps but uh, yeah, Koko is not the thing I hard in on Weavile with lmao. Amicable hard worker.

Someone once told me that "every good offense in SS needs Scarf + Future Sight Lele or its' a bad offense" and honestly I can't blame them for thinking that. Lele is terrifying; Setting up Future Sight is good but its' one of the few special attackers in the dex that actively helps to make Damage stick which is invaluable for a lot of offenses to even operate properly. Specs is terrifying, 4a Twisted Spoon will sometimes kill half a team without even being touched, the sparse taunt Calm Mind set up is great. While she does not appreciate the tiers' obligatory steel type nowadays being left in the hands of Melmetal I can't not put her in the A+ cluster, Lele is fantastic.

This thing has 3 STABs it feels like. Scarf is the most consistent set but legitimately anything works with Kartana and I feel like it is relatively unexplored in what it can actually do. SD Life Orb demolishes a lot of stall teams and Band can do similar results damage wise. It does not appreciate Torn T being on what feels like 2/3rds of teams. It can be a little finicky to build with but its' well worth the effort. Kartana is good.
A

Honest is the word I'd use to describe Tapu Fini. Some players really put Fini on a high pedestal and I don't really share the sentiment personally. She has awkward match ups into everything above her barring Weavile, Urshifu and Heatran. I won't put her any lower though; Fucking with 3 elite level threats in OU is nothing to scoff at. I think Trick + Defog is an awful application of Fini, I think the SM standard of Taunt + Scald is incredibly consistent, the sparse Calm Mind set up is good. She is good on the teams she shows up on and I like her when she does show up but I don't think she fits in the A+ basket of Pokémon.

I've rated Dragonite harshly in the past but I do think it holds some untapped potential still. Turning one of the scariest situations of the game (Shifu + Fsight on preview) into a set up opportunity is valuable. Its' best application has been DD when paired with Ferrothorn and its' surprisingly consistent at wiping out a lot of offenses if you don't give it some level of respect. With how much statuses it it does become aggravating to pilot though; I could not tell you the number of Dragonites I've seen die in an embarrassing fashion to some random utility option along the lines of Zapdos with Toxic.

Grassy Terrain is what keeps a B+ mon in A rank. I have soured immensely on Band Rillaboom; I think it is, ubiquitously, a flawed set that can only go on specific offenses. Bulky SD is excellent at eliminating cheese and helps keep HO well in check in the meta-game and its' utility in item removal on top of being a win con is good. But when it comes down to what Rillaboom actually does in any given game it mostly comes in, sets grassy terrain then leaves so its' other teammates can abuse the terrain it sets (Kartana being a proprietary example, Heatran another.)

...Which leads me into the next Pokémon in the A category. Blaziken is fucking, ridiculous. With Grassy Terrain up this thing feels like it gets an absurd amount of positions to set up and win off of. Its absolute worst quality in all honesty is mostly due to how restrictive it is to build Blaziken; Rilla+Blaziken is incredibly strict in its' formatting and is what holds this mons incredibly specific niche firmly in check. Blaziken is good though; No sane player plays foolishly when they see this off of preview.

Slowbro sets future sights. Slowbro scald fishes melmetal. Slowbro eats up Future Sight. Slowbro teleports as you use U turn. Its the last popular vestige of the Futureport strategy and its' remarkably consistent at the job still.

I can't begin to tell you how many teams I've built and thought on reviewing the six are Volcanion weak. Its' probably way, way, way too many to be honest. Volcanion with Specs can often pick and choose what it wants to kill but it suffers mostly from how reliant it is on good defogging and it does not appreciate how much in the metagame at the moment likes to slot "random" toxics. Give Volcanion any room though and it will in fact kill you. This much remains true.

Pex is weird to rank but I decided to toss it into the A category since its' still remarkably annoying to kill. The adaption of Light Screen + Shed Shell + Knock Off towards the end of CG and in modern tournaments ended up revitalizing stall to a large extent and you should always play with some respect to how fucking annoying Pex is as an anti-tempo Mon. Does it appreciate Lele becoming more popular? No. But its' still Toxapex. Many games throughout this tiers history have gone down to someone running the "unoptimized" standard Scald/Knock Off/Haze/Recover set.

Tyranitar is B+, Excadrill is B, Sand is A tier. Sands consistency and litany of builds available is a massive plus in a tier where HO is incredibly sparse. Excadrill acting as an offensive speed check that spins is incredibly valuable, Tyranitar being a nuclear warhead choice band user that checks Dragapult is valuable. Lumping the two of them together under the moniker "sand" felt fitting.

Corviknight is A in the builder, C- in active play. It defogs. It defogs ten trillion times, it roosts ten trillion times. It U-turns for 2% damage then roosts again. It ID Presses the Rillaboom then gets sacked once the opposing rocker is dead. Nothing happens when Corviknight comes out and I wish it did something past its' job. A tier.

Blissey at large is a fine little blob and does a lot; Being a stopgap to every special attacker barring Lele is very useful. I'll use Blisseys segment more so for elaborating on stall more than Blissey and its' why I put her into A tier.
I don't really share the cynicism some player have towards Stall. Stall and Stall-like teams show up way too much for me to consider Blissey and what it enables lower than A tier; In tour play I've spotted it enough to respect its' inclusion and in high ladder games its' remarkably consistent compared to Stall in its' sister generations of ORAS and SM. It takes effort and specific line ups but due to the success people have had throughout the generation I can't actually call it bad or unviable. Blissey sits in A tier for this reason but it can definitely be discussed at large.
The rest of these will be pretty broadstrokes with some sparse elaboration on noteworthy Mons.
B+ These things are flawed but incredibly strong in certain teams

Can either spend entire games pressing recover doing nothing or hard-walls every single thing it resists or checks. Consistently strange but I trust the slugster. I am a slug believer.

solid but specific.

Some people make incredibly good use of Buzzwole, I am not one of them. Its' solid but easy to abuse.

Veil HO? Sucks. Zolt Hail? Awesome but hard to build.

Brutalizes standard offense. Is incredibly bad into stall.

Reliable to a fault.

Horrifying off of proposition, easy to outplay due to how SS works. MU moth is MU moth.
B Perfectly fine choices with very apparent positives and very apparent negatives tied to them.

Does not vibe in Melmetal city anymore. Corviknight is already sparse. Can be decent still if you're building it to kill Ferrothorn, not steel birds.

Some players preach this thing being nuts, I don't see it. Still solid sparsely.

Overhyped but okay. Ripping a big fat hole through Clefable reliant teams is funny but it dislikes Torn T removing its' item and making it redundant. The Ice Beam calc on Torn T is depressing.

Can steal games on a cointoss but its' inconsistent to a massive degree. I avoid this thing like the plague in the builder.

No Zapdos on preview? Decent. Zapdos on preview? 5v6.
B- Inconsistent but powerful in specific circumstances.

Incredibly volatile balance breaker.

Similar to celesteela but this breaks bulky offense.

similar to toxtricity but this breaks (some) stall teams and bulky offenses.

Second worst OU mon. Incredibly asinine in specifics for an okay at most end result.

Lele check that gives Toxapex room to click better buttons more safely.

Okay in the vacuum due to the check list being fine but in active games its' pretty disappointing.
C+ Incredibly inconsistent outside of specific teams, have to be built with to utilize their specifically good traits

Shed Stall, nothing else. Awesome when it works though!

Table Stall, nothing else.

This thing should not be ranked in OU.

Sidegrades Clefable on a few good stall teams.

Shifu check with sleep.

"I am building a stall/sand team and have no actual way of managing Crawdaunt"

Hyper specific stall slot.

Hyper specific Hyper Offense slot to check Weavile and Shifu. Like. Once.

Trick Room.
C Do not use this in OU unless you're playing for fun.