OK, got a lot of noms here, not all of which need to be taken seriously per se. I just want to start discussion on some of these things to at least understand why they are in their given rank. All of these are drops because I think we need those more now, due to rank inflation, or we need more ranks overall (I would certainly be in favor of an S-/A++ rank tbh)
Bisharp A+ --> A
The whole "oh i beat lati and nobody dares defog on me" hype is pretty much over. With its pitiful special bulk, the fact that it relies on 50-50s even against stuff it's super effective against just because of its shitty speed tier, and the fact that similar mons like breloom and diggersby are sitting in B+ even though diggersby is stronger and faster and loom has spore make it not that strong. Its stabs often hit for neutral but not very often for super effective except against ghosts, psychics and fairies (only fairies are relatively common besides latis), so I don't really think it belongs alongside the gods like manaphy, torn-t, and garchomp. It's easily the least scary thing (personally) in the entire A+ rank. The rise of fatchomp, hippo and manaphy hinder its sweepability as it can get walled by these bulky grounds or get burned by scald.
Scizor-Mega A+ --> A
The rise of fatchomp, hippo and manaphy also hurt him, as does the reduction of megagross. Scizor is just so one dimensional; roost and bp are a given, then it has sd, knock, superpower, bug bite, defog, u-turn. No other options and all sets have the same checks and counters. Scald burns are annoying. I like it vs weavile but otherwise I think it belongs near gliscor, another bulky sd sweeper that doesnt take a mega slot, as opposed to with char x, a far scarier sweeper. A bulky sweeper, sure, but the stone puts 20 points into special attack. It's just not the best, especially now.
Latios-Mega C --> unranked or D
252 SpA Life Orb Latios Hidden Power Fire vs. 8 HP / 4 SpD Abomasnow: 390-463 (120.7 - 143.3%) -- guaranteed OHKO
252 SpA Mega Latios Hidden Power Fire vs. 8 HP / 4 SpD Abomasnow: 352-416 (108.9 - 128.7%) -- guaranteed OHKO
It's weaker on the special side.
252 Atk Life Orb Latios Outrage vs. 8 HP / 0- Def Abomasnow: 281-331 (86.9 - 102.4%) -- 18.8% chance to OHKO
252 Atk Mega Latios Outrage vs. 8 HP / 0- Def Abomasnow: 277-327 (85.7 - 101.2%) -- 6.3% chance to OHKO
Weaker on the physical side.
Mixed is barely stronger if you have very specific EVs, but is that worth a mega slot? If you want the bulk from the stone, use Latias. This thing has no niche, no analysis, no legitimate usage, except for a bulky mixed attacker that lures heatran. Even that role has competition from Altaria. I'm OK with D as opposed to unranked, but C is way too high; there are actually good mons there like Goodra, P2, and Coffin. Even Verlisify knows this; he tried to make it bulky since he noted that it was weaker than regular latios. Kyle Cole summed up why this thing sucks so much, go watch his video if you haven't.
Magnezone B+ --> B
It's just so slow even with a scarf, and the hidden power nerf makes hp fire pack to small a punch, even if they have a ferrothorn. Magnezone is just a bit too niche I feel, and some steels, like tran, completely annihilate it. I think B+ is a bit too high.
Do all rain mons belong so high? B ranks say a bit more team support and that their positives outweigh their negatives. I think they need more than a bit of team support, essentially never used without politoed. At least drop Kabutops, as Starmie outclasses it as a spinner out of rain. So Kabutops B+ --> B.
Tentacruel B --> B-
People have already talked a lot about this one; hazard removal is everywhere to get rid of your tspikes, and most removers (exca is steel, starmie has natural cure, latis and skarm etc have defog) aren't even affected by the tspikes in the first place. Otherwise I'm using starmie, not tentacruel.
In addition, I agree to drop Celebi, and Rotom-W, but those should go through soon.
As for the discussion points:
Charizard X: A+ > S, Yes for sure, this guy is on par with altaria in terms of a dd set. It can't even get burned by scald. Either raise this or drop mega gyara.
Mega Venusaur: A > A+, Yes, a great check to altaria, keldeo, any other fighting type really.
Amoonguss: B > B-, No way. Amoonguss is really underrated, if venu is rising why should he drop? It's quite bulky, spore and clear smog are nice and foul play is an awesome move to have.
Chesnaught: B > B-, I personally like Chesnaught a lot so I don't think it should drop, but I'm gonna be unbiased in my reasoning. I just think reliable recovery on a spikes mon is nice, and spiky shield + leech seed makes ferro jealous, since he only gets protect. No drop.
(also quilladin is the cutest mon ever)
Quagsire: B > B-, Yeah, status wears quag down so much. Sure it checks altaria and other dd sweepers but things like diggersby can still break through. Just not quite bulky enough to be worth it.
Scolipede: B > B+, meh, hazard removal is everywhere, but at the same time baton pass is a ridiculously broken (also skill-less, stupid, and banworthy) strategy, so neutral here.
Reuniclus: B> B+, A stronger clefable? Sign me up. Weak to knock off? ehhh.... that's why I can't decide
Mandibuzz: B- > C+, I like this burd because knock off on walls is cool, but I don't really care either way
Kabutops: B+ > B, already covered this.
EDIT: Just saw the exca nom, but i think we should hold off on that until we discuss lando-t first. Also medicham is way too high, gallade is better than it for sure and if thats why it rose drop gallade instead. :/