Hi council man here, seems theres been a ton of discussion on the D Tiers and i would like to put some of my own thoughts here too since i really enjoy very niche mons.
D tier
Very alright wall breaker, i thought the rise of balance would bring life to this mon but it frankly just doesntdo enough damage. Choice band struggles againts hazards and still folds to a lot of common defensive mons like gliscor, garg and alo while being extremely easy to play around, even dragapult gives it hell. boots set with morning sun is really neat but doesn't do enough damage to warrant a slot over the other Slow-but-not-that-slow-and-definetly-not-fast breakers in the tier. However it is not so bad that i wouldnt see it being used ever, its still very strong but the flaws are really hard to overlook. I would put it in the bottom half of D.
D Tier
Barraskewda is WAY TOO GOOD to pass up as a rain sweeper, but i can't hate on basculegion that much, the ghost typing for rain is godly since dragonite can effectively 6-0 any rain (theres a reason tera ghost skewda exist) and basculegion is bulky enough and strong enough to 1v1 it. I would say its wave crashes are much more powerful but it needing to be jolly to not lose to iron valiant is a hard sell. I guess you can run it alongside skewda but why run 2 of essentially the same mons when rain has so much more diverse threats that can pair up with one another to hit everyside of the opponents team. Basculegion works as a replacement for skewda that is bulkier and beats dragonite, but its less reliable and also MUCH slower, not a bad mon so prob towards the top of D.
D Tier
See, this mon doesnt look bad on paper. Its super strong, has goated coverage, and beats kingambit but man that speed SUCKS. yea it can destroy gambit, ting-lu, dozo, clod and garg but you fight an offensive pokemon, even something as "meh" as keldeo or scizor, youre in a world of hurt. This pokemon also has a 4MSS where it wants to fit rock tomb, bulldoze, close combat and swords dance alongside bullet seed and mach punch. It has the potential to destroy balance but put it againts any offensive pokemon it just loses. D is the place for it, and its probably somewhere in the middle.
D Tier
AV is pretty nice, but it struggles againts bulkier teams. it can 1v1 any offense but put it up againts anything bulky or can set up a hazard, it just loses. It has the opposite problem as breloom where if you put it 1v1 vs againts any offensive mon, you win, but if you put it up againts anything defensive like ting-lu or garg, you just lose. However, Goodra has far better utility so its probably the best mon in D tier.
D Tier
Hippowdon is a really nice bulky sand setter which can help againts the many physical attacker on the tier. It sets up rocks reliably and can whirlwind off threats. However, it is strictly a worse ting-lu. Recovery is nice but outside of bulkier sand teams there is no reason to use it. Its probably a lower D tier. Its a niche mon on a niche style.
C tier
When talking about H-Arcanine i said "Slow-but-not-that-slow-and-definetly-not-fast breakers", hydreigon definetly fits the bill perfectly as that mon, however, hydreigon is far better than H-Arcanine, it has amazing defensive typing able to resist kingambit, gholdengo, h-samurott and 1v1 Ting-Lu. Good Special attacks to threaten stuff like great tusk, lando-t, and great movepool from flash cannon, earthpower, flamethrower and nasty plot. The best set is definetly Sub nasty plot being able to 6-0 defensive team while not being a sitting duck againts offense like breloom. It has a ton of poor match-up ofcourse like play rough ogerpon, iron valiant, volcarona, iron moth however the benefit it brings far outweighs its flaws. I would rise this thing to C just because of how good it is againts bulkier teams. Theres a reason this mon was top tier in early gen 9 despite the nerf to its movepool from gen 8.
D tier in my heart, but its UR
Iron jugulis used to be a really solid fast cleaner that doesnt lose to ting lu and resist sucker punch, however, as the tier slowly moves towards fat and it having poor match up againts a lot of the new offensive mons (raging bolt, gouging fire, kyurem, darkrai, iron valiant) it has definetly fallen off. I would put it in UR but this hurts.
UR
it had 2 good sets, Throat spray sweeper and defensive rocker. both fell of HARD. throat spray has become way too slow and cant break past so many defensive mons and the defensive set just dies to any fairy (clef and primarina has never been better). easy UR
D
Its a really good counter to primarina but thats it, its far too passive and a lot of the special attackers in the tier can use it as set up fodder or just switch out without being punished. Its niche is still very useful as role compressor but most of time using a combo of 2 mons like clef alo, glowking alo, ting lu dengo to beat special sweepers is just much safer. Useful niche, but is generally outclassed.\
D Tier
knexhawk explain away (TL;DR knock absorber for stall)
D Tier
Do not use pincurchin as a terrain setter, you will lose and have a bad time. use it as a suicide lead to support iron valiant break 2-3 mons with life orb, then have 4 HO mons to your liking, yes still use terrain extender + memento or even try eject button but that cuts down on the iron valiant mayhem a bit too short for my liking. Anyways thats my rant on people using this pokemon wrong since the start of the gen and making it worse than it is.... it still sucks, yea rillaboom fell off but its becoming easier and easier to check iron valiant. While this pokemon can turn iron valiant into a broken Uber for 5-8 turns, some teams just deal with it way too easily letting it only get 1 kill at most, so yea bottom of D.
C Tier
yea this pokemon is good. Defensively it has a great typing which lets it hard counter kingambit and samurott, decent bulk and so many good support move from knock off, encore, rapid spin, roost, u-turn and can even be a sweeper with bulk up or swords dance. It can fit on every team style and it can snowball out of control because of the sheer amount of sets it has, and getting it wrong can easily cost you the game. With that said, its stats are still okay and it doesnt have the best match up into HO with a ton of strong threats being spammed and it does take a bit to get going (even the support sets), so i wouldnt put it higher than C+, but i think C is more fitting. Its a good pokemon you should try it.
UR
Its terrible and outclassed. You want a spiker? Garchomp and Samurott. You want a rocker? Lando, Treads and Glimmora. You want a webber? Ribombee and even Araquanid is there. Tspikes? Meowscarada and Greninja. There is 0 reason to use it now that spore is banned, its so frail and slow you can't get more than 1 hazard up. So yea just use a better pokemon.
C Tier
Stall struggles againts kingambit, samurott and many strong physical attackers, and they often have techs for the metal birds, but talonflame often works as a roadblock because most of these threats can't afford to be burned so just the existence of talonflame makes these threats second guess themselves. Definitely a good mon, bottom of C.
D Tier
It's a tera hog of a sweeper but in the same time it can be deadly in the right match up againts bulky offense, however it is very difficult to get set up due to its poor bulk and middling speed. It also has bad 4MSS so it sometimes have trouble with coverage even if you have tera blast.
C+ Tier
An awesome wall for fat and stall, it can run many sets from the regular knock pivot, subseed, trapper effectively and it is an incredible physical wall againts pokemon like great tusk, kingambit, samurott-h and pairs beautifully with wish alomomola to create an almost unbreakable physical defense combo. It is surprisingly easy to slap on teams as it is a dark type that can wallkingambit, samurott, gholdengo while being able to threaten primarina on the switch and spam knock-off. This pokemon is genuinely underrated, stall and balance alike love having this mon, and the varietyof set puts it as a strong contender for C+ tier.
UR
just dont.
Always got basculegions feminine counterpart for special sweeper in the rain. All of the ghost/water typing fun but none of the overlap with the barracuda as it fills the physical role.
Begs the question of where folks feel the lady ghost of swift swimmers belongs in terms of her viability