OK time for some most likely unpopular opinions :/
S ---> A+
Personally I agree with Sir Kay's point that gatr should move down from S rank. Although it is true that you will have problems with gatr if you do not bring some proper stops to it the thing is... if you don't bring those stops to gatr then you would probably get destroyed by many other water type sweepers as well such as samurott, gorebyss, carcosta, or even barbaracle. Gatr is definitely agreed to be the best of those but the checks are necessary on your team whether feraligatr is in the tier or not.
Also on top of that I wouldn't consider the dragon dance to good considering aqua jet hits most things that out speed gatr and when people set up with gatr people will switch into things with enough bulk to handle sd gatr. The extra speed would end up quite irrelevant at that point.
A+ ---> A
As good as seed is with it's and good at setting hazards it is I think it should move down.
Yes it is good. It has access to both stealth rock and spikes. It has amazing bulk before getting hit by knock off and it's ability is EXTREMELY annoying on it making it unbeneficial to u-turn on on it especially with hazards up which it is good at doing itself. It can also use leech seed for annoying recovery.
However you really can't just overlook the lack of offensive presence in an A+ ranked mon. It has nothing to get past xatu or even get any momentum for the team off of it. This creates a huge problem for seed teams. Also when u get rid of hazards via defog or rapid spin which has become highly possible now that people have learned to play around things like pawniard and spiritomb is no longer in the tier.
A+ ---> ???
I keep seeing people talk about how good this is and how it should stay in the same ranking as typhlosion. But whenever I use this or play against it... it is just extremely easy to deal with. Unless your opponent plays it perfectly it can be quite easy to deal with, which is true for many things between B and A rank. To be honest I really don't understand why it is over hyped. Not that it's a bad mon I just feel it is way to high for it's uses.
A+ ---> S
I know this point was already brought up but I think uxie deserves to be with her sister considering it runs so many great sets that can support teams like dual screens, stealth rocks, memento, u-turn, knock off, heal bell, yawn, t-wave, toxic and basically anything you need to fill in the gaps on your team. People have even got calm mind uxies to work and they seem to work better then calm mind mespirit (In my experience).
A- ---> A/ A+
Oh my god this things niche just works so well. As the only magic bounce user in the tier, bar natu, this can solidly switch in on any spike setters that are commonly used in the tier, IE: Garbodor, ferroseed, Crustle, Quilfish, Dragalge, and Weezing. Although there are some mons that set rocks that are too dangerous for xatu to switch in that doesn't really make it's benefits, as a switch in with offensive calm mind presence, irrelevant.