It's better that I exaplained why I made those decisions.
Cloyster C+ If you make Coyster set up you have to deal with it. Which is not that difficult given that he could set up on physical attackers or use a Focus Sash. Shell Smash at +2 outspeed all the metagame and after that, his Icicle Spear, Rock Blast hit hard. For the last slot, you can chose priority or Water STAB.
Smeargle C It's effective is doing what he runs because of his unprectability and because the ability of run Spore/Dark Void. Focus Sash guarantees that Smeargle take a hit and do partially it's job. It has terrible stats as we know.
Donphan B- Donphan is one of the better spinners. It's has good defense and can patch his Special Defense with Assault Vest (Rapid Spin is compatible). Excadrill is not always a superior spinner because his relative fraility and because it's still rather slow and super-effective attacks are everywhere.
Jolteon D I think that Jolteon have a niche over Mega Manectric in the fact it doesn't require a Mega Stone and Baton Pass.
Hydreigon B- Fairies demolished it hard (and if you use Flash Cannon, good luck 3HKOing Sylveon) but he can potentiually 2HKO the majority of the metagame easily and his movepool is unpredictable. Also, becauseit's a 600 BST Dragon it's useful. Also, A Dark type that is so useful this gen.
Jirachi B+ Jirachi is nerfed with being weak to Ghost and Dark but I think that Jirachi has a lot of threads it still resists, it's unpredictable as fuck (Jirachi has around 20 viable moves), more than decent defenses, and an excellent annoyer.
Gastrodon C She has a niche in being a Water/Ground pokemon that is inmune to water attacks and has reliable recovery. Grass are rare because many of the top threads resists it (and some doubke resist it). He has decent defenses (specially his HP) to take some attacks and physical sweeper risk Scald hax.
Metagross C Nerfed so bad with Ghost and Dark weakness but I think that she has a niche. Metagross is bulky on the physical side, has a great load of resistances it can switch in, has Meteor Mash to attack opponent, can use Assault Vest sets, it's a good Stealth Rock setter.
Umbreon C One of the better mixed walls of the metagame. True that it has no offensive presence but he can run Foul Play specially now that hits neutrally Steel types. And now his Moonlight can be considered "reliable recovery2 with the nerf of weather.
Porygon2 B- Evolite Trace Porygon2 is great in this metagame. Exist Knock Off but the common Knock Off users are detectable. It's a good mixed wall with the ability of coping abilities and has some offensive presences. Don't ignore that this type is one of the two only types to resist Ghost.
Magnezone B Steels are in this metagame rampant, and some of the pokemon it used to wall are still in OU to be trapped. It has some myriad resistances that makes it good vs some non-Steel threats, etc.
Reuniclus C+ Clefable has better typing but this is no crap. Clefable doesn't have 125 Special Attack and Reuniclus has better defenses to take hits. His main point is the Trick Room Life Orb set, capabel of taking many threats with moves of his good movepool.
Darmanitan C 140 STAB + Sheer Force really hurts and makes one of the few Choice Band/Scarf best moves in the metagame that is capable of 2HKOing resists of it. IUt has a good movepool to support his Flare Blitz which Super Power, Rock Slide, Earthquake, Thunderpunch, etc. Also moves affected by Sheer Force don't receive Life Orb recoil, remember.
Haxorus C+ Dragon/Ground w/ Mold Breaker with Poison Jab to hit fairies (in the physical side) is Great. 147 Attack with the threat of Dragon Dance or even Swords Dance is nothing to scoff off. His fraility can prevent to reliable DD, it's outclassed by Garchomp or Dragonite partially and Fairies really nerf it. I count on C+ because I expect two oif the Steel types of the top to go to Ubers.
Aggron B- (Mega) A Mega with 230 Base Defense, a maximum of 1,5x weakness and still 140 Attack and average HP is still good. This can be 2HKO by a very few physical threats in the metagame (and one that can it's expect to be Ubers soon). And Steel is way better offensively than Rock/Steel.
Crobat C+ Crobat has a decent support movepool and can make good function as a lead. Flying STAB are good for offensive presence, it's one of the faster Taunt users, has good typing with a lot of reistances (many being duble ones), and has unpredictability of being a lead set or a more offensive set.
Kingdra B- CritDra hurts. Guaranteed 2.25x Draco meteor are not funny to anything that is not Chansey, Blissey, a Steel wiuth Special Defense or a Fairy. But Fairies risk a 2.25x Hydro Pump in their face, same with Steels. Also, there's the threat of rain Kingdra with it's devastating as always, specially if you miss Azumarill.
Weavile B- Dark Buff, Knock Off buff, Icicle Crash, faster priority and the rare 125 Speed tier. Weavile is viable now as a revenge killer. He is frail (although 70/85 in the special side is not that bad) but his goal is being a cleaner of slower threats, not taking hits.
Ninetales B Sun is still good and Ninetales has one gimmick over Charizard-Y: Heat Rock. If you are using a Sun team, you have to use Ninetales if you don't want to be reliant of manual sun. Also Ninetales is good at taking special hits and his Sub Fire Blast and Solar Beam hurts.
Nidoking C Sheer Force and his movepool is scary, even more now that his attack is buffed to bypasses the 100 mark. It's very unpredictable in his movepool that you should be noted if yNidoking is ohysiuca, special, mixed, has Stealth Rocks, etc. There are better sweepers and wall brekaers but Nidoking is not trash.
Milotic C May be even C+. It's viable now specially with status being rampant right now . Water type is the excellent type of always, and it's still one of the best mono type in the metagame only behind Steel or maybe Fairy. Physical attackers fear Scald and Marvel Scale, while Speciall Attacks have to deal with 95/125 defenses (which are great). And it has reliable recovery in the form of Recover.
Ampharos B- (Mega) Electric/Dragon is not a bad typing. Even less in this metagame. 165 Special Attack and Mold Breaker HURTS. Ampharos has almost perfect synergy using Electric and Dragon attacks, has more than good defenses 90/105/110, 6 resistances. It's slow as fuck but his great defenses patch that, and if you deal with Trick Room, be prepared that the speed is inverted and then it will take care with your lower speed.