I'm gonna see if I can try and get ahead of LBN on this one and just kinda go over what these new changes will mean for the tier.
TLDR: Offense of all kinds has become way more honest and will have to be structured differently than what most builders experienced with this tier are probably familiar with. No more Tera Blast to save your mons from being walled. Additionally, with Yanmega and Comfey dropping, BO and Balance get fun new tools, since spoiler alert: without Tera Blast both mons cannot fulfill their HO roles anymore.
THE CHANGES:
Tera Blast, as per OU's prerogative, has been BANNED to the joy of many (sorry canard)
Armarouge has been BANNED (sorry canard)
Comfey and Yanmega are UNBANNED from RUBL and will be rejoining the tier
TONIGHT'S BIGGEST LOSERS:

These guys pretty much relied on Tera Blast to beat their biggest checks, and now they'll be forced to play the same game as everyone else. PZ is sent to low-income housing without the ability for agility sets to beat steels and such, and all tera blast shenanigans in general are off the table, so unless it starts running Tri Attack, its overall damage output is gonna be way less without adaptability sets and TB in general helping it out.

Entei now has to run Tera Grass Trailblaze to beat Quag and Gastro, and is now unable to OHKO either of them, which while this is still strong for Entei, it means that in general the guy can't autowin vs. stall teams by instantly smiting Quag, and has to take a toxic now for his trouble.

Bish no longer can do Tera Blast Fairy / Flying games, so Ches is once again a check. Not the worst punishment, but it def sucks for the guy.

The LBN sample no longer autowins vs. Ches teams. Tort now has zero options to OHKO Torterra, and has to rely on Zen Headbutt to hit the guy at all for a mediocre 2HKO.

Magnezone, like Entei, no longer has the option to instantly nuke Quag and Gastro and kinda doesn't have any options to beat em anymore. Extreme nerf to specs sets.
TONIGHT'S KINDA LOSERS

Bee doesn't get to do QD sets anymore, which while that's unfortunate for set variety, is a win for everyone else with a soul who wasn't running that set.

Cloyster is now honest and cannot nuke Slowbro / Suicune, and has to do so the old-fashioned way, but this guy was lesser seen in the RU scene so he's down here.

Craw really kinda didn't run Tera Blast Fairy too much before, but now you'll have to just run Sludge Wave sets to be able to threaten Ches.

Regidrago is another RarelySeen mon, but Regidrago has officially lost any way of being able to hit fairies with anything more than a tickle.
TONIGHT'S ASSORTED LOSERS

The Tera Blast ghost set is dead now, thank god

no one like ACTUALLY ran Tera Blast Ice Jolteon, but for the few people on low ladder who did, I'm sorry.

CM sets are now kinda dead in the water, and so Mixed Relic Song shall reign eternal (doesn't really matter since it was already the better set but whatevs)

similar to Craw where the Tera Blast Fairy set was a cool thing for it to run, but now it's just gotta rely on the normal tools it already has. Not a massive nerf, but not anything it appreciates losing.

Frosmoth found dead in California

The Armarouge ban already really sucks for snow teams, but Nasty Plot sets are kinda just not now.

Tera Blast Fighting Slowbro. This is the loss that we all grieve the most.
Aside from individual losses, HO in particular, with almost all styles except for Rain, have been severely nerfed with the combo of Armarouge leaving and Tera Blast being banned. Armarouge was an incredibly crucial glue mon for almost every HO team, and now with it gone, the most common fairy, fighting, and fire resist on HO is just not around anymore. Tera Blast being gone also makes it so that HO teams have to rely on their already small pool of mons to now have the exact right coverage, and that's frankly a tall task to ask. I wish you luck Canard. Godspeed.
and I guess onto Yanmega and Comfey, they both were major uses of Tera Blast, and are now both incredibly walled by our Steels. Yanmega, if it wants to do anything it did before, will have to be paired with Trapper Mag to eliminate steels, and Comfey is more of the same.
To adapt, the current discussion and predictions by the Discord (thanks heatranator and gang), are that Yanmega will probably switch from Speed Boost to Tinted Lens and be a fast special breaker for BO teams, with Bug Buzz, Air Slash, U-turn, and whatever else that thing gets. Psychic Noise?
Comfey will probably be a good addition to balance teams, since it gets a lot of pretty good moves, like Taunt, U-turn, Knock Off, and Encore. That paired with a pretty solid priority move in Draining Kiss means that it gets quite a lot of role compression, and will most likely be a very solid mon for teams to run.
uhh as for big winners of this:
Stall and Balance in general are giga buffed, since Armarouge stomped both of them, and Tera Blast was the biggest terror of these teams, since you never knew when some random guy on ladder running Infernape would pull out Tera Blast Electric and nuke your Slowbro or something.
In general since a lot got nerfed by these changes, it also means that previously good mons that were outclassed by Tera Blast gamers like Necrozma could possibly get better due to naturally having the coverage they want, and just being made better by everything else getting worse.
Anyways the tier is saved, and once ladder updates I think we'll see the tier be revamped in a way no one could have ever predicted. Additionally, i KNOW that some guys in UU are gonna become dogshit and are gonna drop as a result, so everyone get ready for more additions to the tier.
Anyways have a great day y'all!