First of all I think the S tier is too small, five is a better number I think. Therefore I think we should add
Gengar for being number one used on blue server, yes theres answers but theres answers for everything. I think with no pursuit being in the game this pokemon is deserving of being on here for sure.
Bisharp this pokemon terrifies me, sucker punch and swords dance together is the stuff of nightmares.
A few more suggestions:
Blissey: I really think this pokemon should be A+ or chansey should be dropped to the same tier as blissey, they are too similar to be different tiers.
Breloom: this should be an A, spore with such high speed is so annoying, theres not a lot of answers to it besides gengar celebi maybe goodra and talon
Mew should be upgraded to A I agree with expendable
Reuniclus should be added to the list I suggest B+ only because its so hard to get as of right now. It has better stats than clefable with worst typing.
Umbreon should be ugpraded to A- or B+ hes a lot better with foul play, great counter to some of the swords dance users.
Celebi and Raikou both to A with reroll tickets I believe all 600 stat legendaries should be A
Serperior to A, I agree with expendable on this one
My downgrades these are most down-gradable pokemon on the list, maybe one or two tier rankings down I'm not exactly sure.
Gyarados: I'm always so happy to see this on the opposing team, its easily manageable and there is just better water pokemon out there (just a worst version of lots of things primarily dragonite)
Milotic: same reasons expendable listed
Weezing: It's stats are just so low
Omastar: Rock typing just makes this worst than kingdra and its infinitely harder to get a good one than kingdra (if thats a consideration on the rankings)
Galvantula: I think this also does nothing, just like what expendable said