Bunch of changes! After a lot of talking and rioting (sigh mence drop :[ ) we are finally here with some new changes. Huge shout out to 
Omfuga for writing the reasoning and the rest of the team! Keep in mind that since tier shifts are happening in approximately 24 hours, all of this is subject to change.
Cresselia A+ -> A
Cress, although massively bulky and sporting an awesome supportive movepool of lunar dance/toxic/twave and sweeping capabilities with moonblast/ice beam/calm mind, as a sweeper it's mostly outclassed by reuniclus or suicune. As a support mon, it's easy to set up on Cresselia with Reuniclus or even cm Florges. Even Feraligatr can sometimes use Cress as set-up bait. Cress has the same problem as p2 in that, even though it walls huge portions of the tier, it just kind of sits there.
Seismitoed A- -> B+
Almost fully outclassed by Swampert. Its only niche is water absorb and knock off, meanwhile it misses out on a significant chunk of extra bulk, ice beam, and roar.
Slurpuff B+ -> A-
It's hard to stop Slurpuff in UU now that it has drain punch. Although Slurpuff has lackluster speed and attack, on top of decent bulk, it's nice offensive typing and fair ability to OHKO most of UU at +6, as well as its ability to set up on common pokemon like Florges, make Slurpuff more than it's mediocre stats. Finally, Slurpuff can now gain health after setting up; for example, if it sets up on a mienshao using high jump kick, Slurpuff can drain punch after setting up on mienshao, and the extra health gained will allow it to take priority hits from the likes of Entei and Feraligatr.
Blastoise Ranked at C 
Great bulk and utility as a rapid spinner on top of being able to check fire types such as Entei, definitely deserves a ranking.
Heracross A+ -> A
Heracross isn't what it used to be. Close Combat/Megahorn/Knock off coming off its nasty attack stat will always be undeniably good, however it doesn't have all the advantages it used to. For example, there are plenty of common mons in UU that can wall Heracross-- namely Gligar, Defensive Salamence, and Florges/Aromatisse. On top of that, it's speed isn't good enough to back its tremendous power flawlessly. Heracross is easy to pick off in UU with Aerodactyl, Salamence, Entei, Crobat, Hydreigon, or Infernape. Heracross is often most held back by its speed, but bolstered by its power. Unfortunately, however, now even Heracross' coverage isn't enough to fully supplement its ability to be revenged easily.
Krookodile A -> A+
Krookodile can trap some of the best mons in the tier. On top of that, using a choice band, its dual-STABs become a nuisance for almost any team. Krookodile is in a pretty good speed tier, and on top of being able to knock off abilities with its main STAB, it hits almost everything in UU with dual-STAB + superpower. With that coverage, you have room for pursuit to trap some of the best psychic types in the tier. Krook also has rocks, which it can run in conjunction with taunt as a good hard-hitting and bulky rocks setter with intimidate.
Feraligatr A+ -> S
Feraligatr is one of, if not the best, sweeper in UU. The thing about sheer force is it allows gatr to put holes into teams without going for swords dances right away. On top of that, after it sd's, Crunch/Waterfall provide near-perfect coverage in UU. On top of that, life orb aqua jets are nice for picking off weakened mons. With pretty good bulk, decent speed, and immense power, with priority to make up for its speed, Feraligatr is a sweeper that has no trouble trucking through most UU teams.
Salamence S -> A+
Intimidate sets are mostly the best ones with mence, and they have proven to be very good, however mence was overhyped when it first dropped to UU. It's very good-- particularly life orb Mixed sets and defensive defoggers, however it's not completely unwalled, either. Moxie scarf is okay, but walled by a lot of things. As for the life orb sets, the weakness to rocks and easiness to wear down, as well as the potential to wall with p2/cress/Suicune make it great, but not S-rank material. As for the defog sets, it checks some of the most dominant threats, but baits in things like florges too easily. Also, it must choose between using STAB, using flamethrower to hit steels, and using toxic and being completely walled by steels.
Lucario A -> A-
Not really seen as much in UU. Luke's biggest problem is 4 move slot syndrome. It has to choose whether to miss out on priority, get completely walled by gligar/mence, or be unable to hit psychic types. One of the cooler luke sets atm is nasty plot, which still hits pretty hard with STAB priority, and catches a lot of teams off guard. Flash cannon can be pretty cool to smack a florges, too.
Golbat C -> Unranked
Mostly outclassed by Crobat. Even the extra bulk doesn't supplement Golbat nearly enough to match Crobat's great speed and attack. Also, as a bulky defogger, Gligar outclasses Golbat.
Fletchinder B -> B-
lol
Qwilfish B -> B+
Great spiker/tspiker that walls Heracross and can spread status. On top of that, lead sets with explosion or dbond can be threatening to balanced/offensive teams.