S Rank

Tangrowth
Kyogre
Arceus-Ghost
Arceus-Normal (best sweeper in the tier, spikes push it from A+ to S)
Genesect
Dialga

A Rank

A+

Groudon (defines an entire playstyle, spdef don is stupidly good)
Giratina-O
Darkrai
Latios
Deoxys-S (best hazard setter in the tier)

A

Latias (better than Palkia cuz faster)
Palkia
Ferrothorn
Arceus-Fighting (spdef ogre, tentacruel, spdef don, latis, can't check darkrai+ekiller reliably so it drops)
Arceus-Steel
Deoxys-A (moves to the bottom of A because loses to a lot of common leads now)
Ho-Oh (requires a lot of support but wins games on its own if SR stays off)

A-

Rayquaza
Tyranitar
Excadrill
Arceus-Grass (one of the better support arceus forms and cm is also very threatening)
Arceus-Water (hard to fit on rain but it checks a lot of important threats and SD can be cool also)

B Rank

B+

Kabutops (drops cuz it loses hard to bulky donner, gira, and isn't an ekiller check at all)
Skarmory
Tentacruel
Arceus-Dark (hard to fit but can quickly sweep you if you're not careful)
Accelgor (one of the best leads in the tier...pls don't use u-turn tho)
Froslass
Heatran
Gliscor
Zekrom

B

Terrakion (moves to top of B cuz decent cleaner + soft checks rai and ekiller)
Cloyster
Landorus (cool scarfer on sand, way better than C)
Shaymin-S
Mewtwo
Forretress
Arceus-Electric
Arceus-Ground
Giratina (fast dual phaze is decent on hazard stack)
Arceus-Rock

B-

Espeon
Omastar (getting outsped by genesect in rain is no bueno)
Wobbuffet
Ludicolo
Kyurem-W
Tornadus-T
Kingdra
Salamence (hard to fit, but outspeeding gene + moxie is actually pretty dope)
Landorus-T (good in theory, but never really seems to do much)
Blaziken
Kyurem-B

C Rank

C+
Xatu
Lugia (drops because it's not even that great of a wall)
Reshiram
Smeargle (smashpass is a thing, no matter how mu oriented it is)
Arceus-Dragon
Abomasnow
Gastrodon
Shiftry
Victini
Tornadus
Sableye
Arceus-Psychic

everything else is not worth ranking imo. Hippo is trash, jirachi is bad, deo-d doesn't really check anything and ends up being an inferior deo-s cuz u sack it for hazards, garchomp is an unmon that's only used cuz it looks cool