With Terrakion discussions out of the way, let me give my 2 cents on some mons in the current meta -
Rises
-> S
As Clone mentioned
here, Air Balloon Eruption Heatran is an absolute unit that near guarantees rocks by nuking most common defoggers like Corviknight, Tornadus-T, Landorus-T. Adding its standard SpDef set as well as Flame Body physical set to the mix, it's extremely versatile Pokemon that can be tailored to make progress or outright beat any Pokemon in the metagame (except something like Heal Bell + EQ Dragonite or Rest TankChomp, which are anyway very niche options on Stall)
-> A
Think Volcarona can't make any progress against Heatran? Think again -
https://pokepast.es/d74bad52c3787072
The set mentioned in this paste means that Volcarona can Sub when Heatran switches in, then QD in the next turn, at least once initially if Heatran uses Taunt. This means that Heatran cannot break its subs, and Volcarona can just sit and wait for the next opportunity to QD, hitting Heatran with boosted Psychics in the meanwhile, to 1v1 and beat Heatran in the long run. While the set needs heavy Hazard Removal support and the whole team built around it (as perfectly built in the above Team Paste), the fact that Volcarona can legit attempt to beat its most popular check warrants a VR rise in my eyes.
-> A-
As far as I see it, B+ seems to usually include Pokemon that fit only 1 archetype but are excellent on that (like Hawlucha on HO, Gastrodon on Fat). Thus, G-Moltres's inclusion in B+ made sense when it was assumed that it only fit HO as a deadly sweeper that checks Ghosts like Dragapult. However, based on my own experience, as well as recently released samples and tour matches in the past few months, Moltres-Galar definitely fits more builds than HO. It is good on Offenses like Rain as a Pult check and stallbreaker, securing 2 key match-ups for offenses. Even on bulky offenses and balanced teams, it has been seen using Chesto Resto sets to offset its lack of recovery, and could perhaps use a RestTalk Mono-attack set to act as a late-game wincon on Fat teams. It is also one of the better options vs Demon Mew, which few Pokemon can boast of.
-> A-/A
Continuing about Demon Mew - If you lack a Dark Type, Fast Toxic, Taunt, or Trick, you auto lose. Need I say more? Add sets like Hazard Setter on Hyper Offenses as well as Fat Balances to the equation, I think its customizability warrants an A rank, although A- is still not an issue.
-> A-/A
After Kyurem ban, Rain has been a terrific archetype. Pelipper sets rain, and Barraskewda abuses it to 6-0 any team lacking a bulky water resist like Slowbro or Toxapex. Thus rain in itself deserves a huge rise in VR.
-> B/B+
Seismitoad is very good on rain teams due to access to Stealth Rocks, ability to outspeed most of the meta, as well as being able to beat Barraswekda checks like Toxapex.
-> B-/B
While not bringing as much utility as Seismitoad, Crawdaunt boasts of only one thing - terrifying wall-breaking. In rain, it can 2HKO typical Barraskewda checks like Toxapex if unboosted, and has a strong chance to OHKO if boosted.
Drops
-> A-
With Heatran as the premier Stealth Rocks setter, Corviknight is no longer the best defogger in the tier. Magnezone's presence doesn't bode well for it either. It also hates the rise of other Electric types like Zapdos, Rotom-W. Further, breakers it's supposed to check like Kartana, Garchomp, Tapu Lele all have means to beat it, and if these are paired together, it gets easily overwhelmed. It may check ground types, but it's outclassed there by Slowbro who is less passive against ground types with access to Ice Beam, Scald, Future Sight, and an even slower pivoting move.
-> B+
Hail is in a tough spot right now due to the revival of rain, double Steel cores, equipment of Choice Scarf by Kartana, Tapu Lele etc.. Hence, Arctozolt belongs in B+ rank, a spot shared by mons who are great in a single archetype only. A similar case could be made for A-Ninetales, but IMO it should remain where it is, as it glues together Screen Hyper Offense in addition to Hail (as witnessed by its SPL performance)
-> B/B-
After Kyurem ban, Blissey has absolutely no place on not-fat teams, as it is too passive to do anything noteworthy (it has literally 0 usage in SPL -
https://www.smogon.com/forums/threads/spl-xiii-ss-ou-discussion-thread.3695044/post-9079794)
-> B+
Same goes for Scizor, as its main niche was to check Kyurem. But, it can still sweep with its SD sets on Hyper Offense, while soft checking stuff like Tapu Lele, Kartana, Weavile to generate momentum with its defensive sets. Thus I believe that it shouldn't fall as much as Blissey.