im curious about the drop of Excadrill and Rhyperior, Excadrill is still strong as a sand sweeper being able to take care of most teams and even its checks with help or even as a lead on HO teams, and Rhyperior can still be useful as a check to Heatran and Volcarona
Excadrill is easily walled by common physically defensive mons like Corv, Skarm, Buzzwole, Tangrowth, Rotom-W and Landorus-T, and revenge killed by common priority users like Urshifu and Weavile, so it doesn't always do much. Rhyperior is just a relic of Rotom-H days - we have Heatran and Dragonite to check Volc, and Dragonite, Garchomp, Slowking, Fini and others to check Tran now.
I think the rises are just about what was being expected but Vic and Blace are 2 mons I am still a bit curios about. Most of the mons that rose haverreded screens setter on teams. Wonder about this too.
why did blacephalon rise? seems worse than the other fire and ghost types roaming the tier
Victini is played as a moderately fast offensive pivot with some useful defensive utility (checks Clef, Scizor, some Volc sets, etc). Blacephalon is just an insanely powerful Choice Specs wallbreaker with few switchins - I recommend looking at WcoP replays, and it's probably part of the reason Kommo-o rose as well.
Grimmsnarl has a solid niche over Koko in checking Dragapult, which is the worst Pokemon for screens teams to face as it outruns nearly everything viable and hits through screens with Infiltrator.
Why did Weavile rise, but Bisharp drop?
How did Pex rise back to A+? Future Sight is still rampant, and Heatran is as good as ever
Also, why did Bisharp fall to A-?
WCoP is your friend here again - Weavile has a way better offensive typing than Bisharp, a much better speed tier, and isn't forced into the same mindgames against Dragapult. Bisharp had pretty poor winrate in WCoP Round 1 and seems to be mostly outclassed by Weavile at the moment.
Toxapex provides a check to rising threats like Weavile and Urshifu as well as the ubiquitous Dragapult, and you'll see in WCoP Future Sight is declining heavily at the moment, like Finch explained above.
What's the rationale behind Amoonguss dropping? I'd imagine it'd be doing better rather than worse now with the rise of Urshifu-R and Fini and the constant demand for Knock Off absorbers, I've used it a decent amount and it's still quite reliable.
Amoonguss is outclassed by Toxapex and Glowking as Regenerator Poison-types, and Tangrowth as Regenerator Grass-type, which can cover most of the stuff it checks well, and crucially, unlike Tang, Amoonguss can't check Kartana without HP Fire, or Ground-types at all. Its main niche over them of Spore isn't so useful in a tier where Tapu Koko and Tapu Fini are pretty common as well. The role compression it provides if you're really desperate for it is enough to keep it ranked, but you'd almost always be better off with something else.
Why is mimikyu unranked? I know its not that good and usally outclassed but i figured disguise, ghost priority and sd along with good utility moves would give it a niche? Something i missed in the meta maybe?
Also recently got it on my switch and i have been keen to use it alongside clef and dragopault as a sorta ghost/fairy spam thing.
Mimikyu sadly is just too weak, slow, and frail to be useful in OU. Try Aegislash for a Ghost with Swords Dance and Shadow Sneak, which is slower but has the bulk to utilise its solid defensive typing to set up, is way stronger, and also can get fantastic coverage with Ghost STAB + Close Combat.