S Rank
Reserved for Pokemon that are absolutely meta-defining. These Pokemon are able to perform a variety of roles very effectively, or can just do one extremely well. Their use has low risk involved and high reward exerted. Pokemon in this rank have very few flaws that are patched up by numerous positive traits.
S

Piloswine [Eviolite, Choice Band, Icium Z]: has super effective stabs against rhydon. risky to setup with sd.
A Rank
Reserved for Pokémon that perform extremely well in the metagame. These Pokémon are typically considered excellent Pokémon let down by a few faults, thus keeping them out of S Rank. They typically require more support than an S Rank Pokémon, but nonetheless are very effective.
A+

Electabuzz [Fightium Z, Eviolite, No Item] fightium z focus blast, or simply focus blast

Golbat [Eviolite] -

Gurdurr [Eviolite, Flame Orb] BU+Drain Punch

Misdreavus [Eviolite] wins cuz levitate+shadow ball / WispHex / whatever

Qwilfish-Hisui [Eviolite, Darkium Z, Poisonium Z, Waterium Z] (z)waterfall

Wartortle [Eviolite] lol
A

Frogadier [Eviolite, Focus Sash, Waterium Z, Heavy Duty Boots] lol

Raboot [Choice Band, Fightium Z, Firium Z, Heavy Duty Boots] HJK go brrr
Rhydon [Eviolite, Choice Scarf]

Servine [Eviolite] lol

Thwackey [Eviolite, Grassy Seed] lol
A-

Corsola-Galar [Eviolite] whirlpool, strength sap

Duosion [Eviolite] fsight or whatever move

Sliggoo-Hisui [Eviolite, Steelium Z, Life Orb] (z)flash cannon

Hattrem [Eviolite] psychic / giga drain

Machoke [Eviolite, Icium Z, Flame Orb] dynamic punch / cc etc. lol

Magmar [Fightium Z, Firium Z, Sitrus Berry, Eviolite, Heavy Duty Boots, No Item] (z)focusblast

Mareanie [Eviolite] cant switch in

Roselia [Eviolite] lol

Tinkatuff [Eviolite] encore, cant set up

Tangela [Eviolite] LOL

Vigoroth [Eviolite] taunt bu
B Rank
B Rank Pokémon are typically considered good, but overall quite niche, and require much more support than a Pokémon in A or S Rank. Their flaws are also much more prominent than Pokémon in S or A Rank, making them less effective overall
B+

Clefairy [Eviolite] -

Crocalor [Eviolite] wisp, risky switch in

Dunsparce [Eviolite] earth power

Fraxure [Eviolite, Steelium Z, Choice Band] low kick / iron head

Gabite [Eviolite] eq

Klang [Eviolite] magnet rise ggrind

Lampent [Choice Scarf] energy balls

Marshtomp [Eviolite] scald

Monferno [Electrium Z] cc

Naclstack [Eviolite] bad

Pawniard [Eviolite, Steelium Z] iron head, cant switch in

Rufflet [Choice Band] cc

Vulpix [Heat Rock] energy balls
B

Combusken [Eviolite, Firium Z] cc

Dartrix [Eviolite] lol

Drakloak [Eviolite] ???

Girafarig [Eviolite] special attacker

Glimmet [Eviolite, Focus Sash] ep sash debris. lol

Hakammo-o [Eviolite, Steelium Z, Dragonium Z] FIGHT

Ivysaur [Eviolite] lol

Morgrem [Light Clay] ???

Quilladin [Eviolite] LOL

Swirlix [Grassy Seed] get surf'd
B-

Ferroseed [Eviolite, Focus Sash] lol

Fletchinder [Eviolite] wisp...???

Krokorok [Choice Scarf] eq

Magnemite [Eviolite] get beam'd

Metang [Eviolite] um

Murkrow [Eviolite, Choice Scarf] um

Palpitoad [Eviolite] whys this ranked

Quaxwell [Eviolite] lol

Sliggoo [Eviolite] can fit coverage

Toedscool [Eviolite] lol

Zweilous [Choice Band, Eviolite, Darkium Z] uh
C Rank
C Rank Pokémon are generally mediocre in the metagame. They typically require much more support than Pokémon higher up the viability rankings, although they can still be effective in the right circumstances.
C

Gastly [Choice Scarf] eball

Lairon [Eviolite] ?

Mienfoo [Choice Scarf] hjk or w/e

Seadra [Eviolite, Life Orb] lol

Vullaby [Eviolite] ok