If we don't have a B assume everything in B+
Aerodactyl
B dactyl is a great mon. It offers edgequake coverage, (rock slide in this case with a 50% chance to flinch at least one mon) tailwind, taunt, and wide guard. However it is very frail,doesn't have too great of a typing,a and is somewhat forced to use a focus sash. It can't fit all of the support moves above so you'll have to pick according to your team.
Arcanine
B+ Great defensive mon. It has morning sun, will o wisp, heat wave and other coverage attacks like wild charge or close combat. It's great as a support mon with offensive pressure or just fully offensive.
Breloom
B Spore. Just spore. It's decent speed and 100% accurate sleep move is amazing in this meta to create free turns. It also has great fighting coverage for mega kangaskan and other things like Tyranitar.
Charizard (Mega X)
B+ Zard X isn't all that bad. It hits really strong but it's basically a poor mans Mega Salamence. It can function as a Dragon Dancer but is held back by its bad pre mega ability and weakness to Landorus-T. Would like to see a bulkier Will o Wisp.
Conkeldurr
B+ I am a hug fan of Conkeldurr. It beats Bisharp, Kangaskhan and can ice punch mega mence. The only thing holding this thing back is intimidates and Sylveon spam in the meta. Iron Fist and Guts are too great abilities also.
Entei
B- Entei is somewhat of a lesser Arcanine as a support role. But it's offensive variant isn't bad at all.
Ferrothorn
B- ferrothorn doesn't seem as annoying as last ten with Low Kick Kang, powerful Knock offs, etc... It's somewhat a physical Venusaur and just annoying in general
Garchomp
B Honestly doesn't deserve the hate. It's just a weaker Landorus, but it's in a better speed tier and can run Substitute, even Swords Dance and has dragon coverage. Picking this over Lando T is very situational
Gardevoir
B- Gardevoir was a world champ last year because there weren't too many fairies but now we have Mega Altaria, Hyper Voice Mega Gardevoir and the ever present Sylveon. It's Scarf variant doesn't hit hard if the move is nt super effective while its Specs version is too slow. Can still run support with Will o, Heal Pulse, Trick Room, etc... But is greatly outclassed.
Gardevoir (Mega)
B+ Finally gets the Hyper Voice it needed. Hits hard af and is faster little frailer Sylveon.
Gengar
A- offensive versions and support roles can be fulfilled greatly by Gengar. Holding it back is Bisharp and generally being frail.
Gengar (Mega)
B+ Using this over Gengar for offensive or support roles is kind of dumb. Offensive variants are still good but you are better off using a different mega and normal Gengar. Still a great perish trap mon tho.
Greninja
B- this boy unlike in OU just doesn't hit hard enough. It faces 4MSS syndrome in this metagame because if it can't hit anything super effectively it's not really too threatening.
Gothitelle
B Shadow tag is still a great ability but it's just outclassed by Cresselia now. The only niche it has over Cress is Tickle and Stag.
Gyarados
B intimidate and bulky water type is great. Ddance variants are powerful and can take dragons decently well. Not a bad mon but there are lots of other options people consider over this.
Hariyama
B- doesn't really have a niche over Conkeldurr other than Fake out.
Hitmontop
B intimidate, wide guard, etc... Great support mon but there are better options teehee.
Hydreigon
B+ Hydreigon isn't too bad. It's specs variant isn't too good due to the speed creep and 4x weak to fairy sucks. Scarf version is still good but just nerfed due to average speed tier.
Latios
B this nigga ain't that bad with helping hand and strong STAB and ice beams. Not bad but has notable flaws such as 4MSS and weak to Bisharp.
Ludicolo
B I'm in love with da Colo. Ass vest is still good cuz ass vest makes it bulk af. It is also great rain mon with ability to beat Swampert and Politoed. Weakness to birdspam is bad.
Milotic
B+ The special Bisharp. It's bukk af and ice coverage along with scald burns is great.
Politoed
B good rain mon and only setter. Asides from rain, doesn't do much.
Raichu
B+ Annoying af. Fake out and encore is hell and boltbeam coverage is never bad. Is great support for its teamate with lightningrod and just threatening encores.
Raikou
B fast snarl, bolt beam coverage. Is kind of like raichu but bulkier, can use ass vest and offers snarl support rather than fake out.
Rotom (Mow)
B it's the rotom with a niche of not resisting birdspam! Seriously though, it's a less spammable rotom that is only seen when it's typing is better for a team. Otherwise go with the other rooms.
Salamence
B Salamence's niche last year was an Intimidate user that went Special, but now there are simply better options. A support role would be cool but that is somewhat outclassed by Suicune. Offensively, its Physical set is lackluster while its Special attacking set isn't as good as Hydreigon's
Scizor
B+ Feint, bullet punch, u turn os really cool. You can beat fairies, ruin protects and grab momentum. A swords dance set wiht bug bite or even trick room option is nice. Very versatile.
Scizor (Mega)
B Mega Scizor is just a bulkier slightly harder hitting Scizor with a 10 speed boost. It takes up the slot of a mega shield ping everything normal Scizr does and isn't worth it.
Scrafty
B fake out, intimidate is a cool combination it has along with hitmontop that is just 4x weak to fairy. It does have a trick room option over hitmontop and can run Lum to be scarf khan.
Smeargle
B Dark Void exists, then Smeargle exists. It has other gimmicks like Transform, Follow Me, and Tailwind.
Terrakion
A- Terrakion has risen due to its ability to beat Mega Khangaskan and Bisharp. It can use Lum Berry to beat annoying status while still hit hard. Rock Slide also has the 30% flinch chance.
Thundurus (Therian)
B Thundurus Therian isn't too bad although it is outclassed by its other form. Volt Absorb makes it a switch in to annoying Thunder Waves and it can be a hit and run mon with Volt Switch.
Togekiss
B+ Follow Me and Tailwand is great. Fairy is still a great defensive typing.
Tyranitar
B Tyranitar is a little bit worse due to Landorus-T, Terrakion and Bisharp. However with Excadrill sand becomes viable, and a support or scarf set isn't bad.
Tyranitar (Mega)
B- Mega Tyranitar had a niche as being a Dragon Dance user with Rock Slide but it has gotten worse with the aforementioned threats.
Volcarona
B+ Volcarona is amazing because it has a quiver dance option and rage powder support. Heat Waves are very good in this meta, especially boosted ones. The bad thing is it's 4x weakness to rocks.
The later stuff will be editted