Note:
I am the sole author of all of these reasonings, and therefore, the opinions of every council member may not be fully reflected.
Rises:

A+ ->
S: Flygon is the best utility Pokemon in the tier, with defensive Flygon sets being the sole ground able to deter Rotom-Mow, as well as checking many threats and being able to check and defog against Copperajah consistently. Choice Scarf sets are also very useful, proving to be one of the best cleaners in the tier.

A ->
A+: Diancie has proven itself as one of the best Dark and Normal resists in the metagame, able to check threats such as Drapion, Exploud, and Braviary. It's able to pressure Xatu and borderline sweep unprepared teams, as well as beat Vaporeon with Skill Swap or assist its team with Heal Bell.

A ->
A+: The usefulness of Vaporeon is debated often, but there is no denying its pressure in the teambuilder, often requiring a check to it to break past balance teams. However, the rise of Vaporeon is still limited by a lot of the council's belief that its passiveness holds it back, making it to where the checks to Vaporeon can use it as setup fodder and abuse common Vaporeon structures.

A- ->
A+: Another vote where the council was split, but most agreed that Glastrier should rise. While the focus during the suspect has been on Substitute Iron Defense sets, which are still rather potent, Substitute + SD sets have been getting a big rise in popularity and have been showcasing the dangerous nature of Glastrier versus common bulky cores.

A- ->
A: Drapion is a rather potent setup sweeper, often causing teams to fold after their single check is crippled or KO'd. Drapion has been causing defensive Flygon to run faster speeds in order to check it, as well as causing the rise of Mudsdale and Diancie to check it, which Toxic Spikes sets can still take advantage of.

B+ ->
A-: Decidueye has seen a rising popularity due to the prevalence of Vaporeon, as well as the amount of teams that are lacking in Ghost resists. Choice Band sets are very potent, as they have a powerful priority move in Shadow Sneak and can take advantage of ghost resists such as Guzzlord with a powerful U-Turn.

B+ ->
A-: People were quick to dismiss Vileplume as a bad Pokemon due to its difficulty as a Fighting-type check, but it has recently seen a surge in popularity as a general physical check as well as a Vaporeon abuser with Growth sets.

B+ ->
A-: Although screens is significantly nerfed with the banning of Light Clay, Xatu has seen a return to form with its traditional role of keeping off rocks, being able to check Copperajah and Bronzong with relative ease. It's also able to check Fighting-types such as Sirfetch'd and Machamp by outspeeding them and using Psychic, as well as Teleport as a slow pivot.

B ->
B+: Mantine is able to exploit common cores with a Grass-type Pokemon as a Water resist, as well as pressure Vaporeon due to its inability to hit it back. Its seen a steady rise in use during NUPL, and its special bulk means that Pokemon such as Salazzle or even Specs Decidueye are easier to deal with.

B- ->
A-: Celebi is seeing a huge rise in this VR, as its ability to setup and sweep teams is nearly unrivaled, breaking through common Psychic checks with Aura Sphere and using Recover and Natural Cure to stick around to do it multiple times.

B- ->
B: Ninjask is able to take advantage of the lack of scarfers in the tier, outspeeding and threatening scarfers such as Rotom-Mow and Passimian after a Protect. It also assists Pokemon that take advantage of its U-Turn switchins, often forcing the opponent to play linearly against the STAB U-Turn.

C+ ->
B-: Araquanid has been a good Webs user, but has recently seen more success with SubToxic variants that aim to exploit Vaporeon and bulky Flygon, as well as hit neutral targets hard with Liquidation.

C ->
C+: Qwilfish gives Garbodor solid competition as a faster Pokemon with a solid niche, having both Intimidate and Scald to scare out physical threats as it sets up Spikes.

UR ->
C+: Jellicent offers a bulky Water Absorber with a relatively fast taunt, allowing it to pressure most Stealth Rock users and Vaporeon, as well as giving it the tools to hard check all Glastrier sets that don't carry Throat Chop.

UR ->
C+: Druddigon has gotten its niche back with Mold Breaker + Stealth Rocks due to the recent rise in Xatu usage, as well as being a niche Sheer Force breaker with the ability to pressure Steel- and Fairy-types with Fire Punch and Gunk Shot.

UR ->
C: Rhydon hasn't seen much use, but its a niche offensive Stealth Rocks user that can pressure Pokemon such as Talonflame or outspeed and threaten Copperajah.

UR ->
C: Silvally-Fairy has seen use on Hyper Offense builds, relying on its resistance to Knock Off and good offensive typing, as well as its setup potential. This allows it to threaten sweeps on unsuspecting teams, especially after other threats break through first.

UR ->
C: Due to the fickle nature of Electric resists, Magneton has found itself becoming a niche special breaker with Analytic + Choice Specs threatening big damage on unprepared teams.
Drops:

A- ->
B: Machamp has a niche in Guts, which allows it to take Scalds without much trouble. However, it is mostly outclassed as a breaker by Sirfetch'd, due to its ability to hit Ghost-types and overall better coverage and speed tier.

A- ->
B: Tyrantrum is a very threatening wallbreaker; however, the rise of Mudsdale, Bronzong, and defensive Flygon in use has seen its threatening nature decline, and although its able to pressure teams when it gets in, its typing and speed tier leaves very few opportunities for it to do so.

B+ ->
B: Dhelmise has seen lack of favour compared to other hazard removal, likely because of its difficulty to fit, the higher amount of preparation for Grass-types offensively, and its very slow speed tier. Pairing this with the premier Fighting-type Sirfetch'd having Scrappy, and Dhelmise has seen less justification to be fit on teams.

B+ ->
B: Escavalier is a good Pokemon, but it often takes the place of very valuable Steel-types that can offer Stealth Rocks, or over the meta-defining Assault Vest Copperajah, all while being hard-walled by Talonflame and Arcanine. This lack of compression has pigeonholed it into requiring niche builds in order to flourish, which is too constrictive for most.

B ->
B-: Aerodactyl has not seen as much recent success, with Sub Pressure sets being difficult to justify and Choice Band or HDB sets struggling against defensive Ground types.

B ->
B-: Passimian is a staple of speed control in NU, but the current state of the metagame often forces it to take large amounts of chip or get predictions correct to make any valuable progress.

B ->
C+: Weezing becomes less justifyable when compared to the other poisons in the tier, as setting Toxic Spikes is much less valuable with the host of good options available to absorb them. Garbodor also does its job of checking Fighting-types while offering Spikes and a check to Toxicroak.

B- ->
C+: Inteleon struggles to compete with Blastoise as a setup sweeper, and tends to lack enough breaking power as a Choiced Pokemon due to lack of a second STAB or valuable coverage compared to Starmie.

B- ->
C+: Virizion struggles with being a Vaporeon check that hates being burned by Scald, while also struggling against the tier's Fire-type and Flying-type Pokemon, which give it very few opportunities to set up.

B- ->
C+: Zoroark has mostly seen use as a Choice Scarfer, due to its lack of power and speed tier to take full advantage of its ability. Therefore, most people regard Zoroark as a "gimmick", and its reserved for relatively rigid builds that try to bait a specific response and rely on these 50/50s.

B- ->
C: Comfey is not valuable as a setup sweeper due to lack of Hidden Power, which relegates it to mediocre Defog and support roles, even though most of the Stealth Rockers in the tier beat it.

C+ ->
C: Absol was a Pokemon we put on the VR due to the ways it can force holes into common cores, but its speed tier holds it back from doing well outside of specific matchups, either giving up rolls with Jolly or being outsped and killed by certain Pokemon with Adamant.

C+ ->
C: Exeggutor-Alola competes in the role of abusing Vaporeon, but does a bad job of this with Choice Specs sets as Vaporeon players can scout with Protect and respond accordingly. Therefore, using it to its fullest potential is nearly impossible.

C+ ->
C: Gigalith simply struggles with too much competition, offering no Ground-type to block Volt Switches, as well as struggling to check tier staples such as Starmie effectively. However, it still has a niche in checking Salazzle, and can still serve as a special wall.

C+ ->
C: Electric Terrain teams aren't that good right now.

C+ ->
UR: We put Arctozolt on the VR with fears of its BoltBeam coverage with massive pressure under hail, and it has shown very little reason for us to still consider it as such.

C ->
UR: With the banning of Light Clay, most of its niche is just done better by Xatu or Starmie as a defensive or offensive Pokemon.

C ->
UR: Although its one of the only Future Sight Pokemon in the tier, it has a lack of pressure towards Copperajah and struggles to break through any team without a significant amount of help.

C ->
UR: This Pokemon is just too weak to serve as much more than a Psychic Terrain or Healing Wish support Pokemon.

C ->
UR: Electric Terrain teams aren't that good right now.

C ->
UR: Silvally-Steel faces competition from much better Steel-types and Defog users, with a very weak Flamethrower not serving as a deterrance to Steel-type Stealth Rockers and being shut down by bulky Fire types.

C ->
UR: Electric-types are good right now, but Vikavolt's reliance on Heavy-Duty Boots and very slow speed tier open it up for exploitation by offensive and defensive Pokemon alike.