Ding dong the rat has gone... to enjoy its retirement because ain't no way it'd ever see use even if there was a Champions Ubers tier.
Ahem.
I don't really think there's any true losers to this ban, since YChu's ban opens open building a lot and there will be less stress on mons that were formerly used to check it. But winners...
:Pawmot:
This mon is not the easiest to build with but it is GOOD. Incredibly potent wallbreaker that can 2HKO most defensive pokemon with LO and its stabs, Ice Punch smashing through most of the remaining answers to its stabs. It does barely miss on KOs vs healthy bulky Chomp but it's hardly a dealbreaker since that takes damage so often. Has a very free 4th moveslot after stabs+ice punch, which there are many good choices. I like Encore, but Mach Punch keeps it from being picked off by Sucker Punch, as even with a resist it's very much frail still and post CC it can be vulnerable to the move.
:garchomp: :hippowdon: :gliscor: :excadrill:
Grounds generally improve if only because they're now less pressured to stay at super high health for a YChu in the back, and thus can focus on checking other stuff. Hippo I feel is especially great since now it has the luxury of possibly flexing between spdef or more of a physical focus, depending on the team's needs. Physdef being a really sturdy stop to Blaziken and ZardX (brokens), also stopping Zabsol cold. Gliscor meanwhile was a very underrated pick even during YChu's time, but it gets better now that it's not forced to be so careful constantly with its health. Strong hazard setter this one, especially with taunt to shut off defog from Corv.
:Metagross-Mega: :Staraptor-Mega: :Froslass-Mega:
Both of these while able to slam YChu hard on a good predicted switch in, hated 1v1ing it. Meta could trade at least, but it would often be paralyzed in the end while Raptor just loses to YChu always. So it leaving is great for both. (btw run Body Press Mega Meta, much better than EQ which only really serves to hit Aegislash). Froslass meanwhile might seem like a weird 'gets better', but it lost not only an offensive check but also competition with YChu's ban. It's quite fast itself, and ice stab is incredibly threatening in this metagame, especially with how many teams rely on Garchomp to glue teams together. It slices right through Corv/Chomp/Glowking structures, and even can burn Hamurott with Wisp.
:Samurott-Hisui:
I guess this is a loser... in the sense that now that it's #1 partner in crime is banned, the spotlight is on it now but eh. We're all winners if this thing gets the boot someday. (I hate this thing even though it looks cool)
Few other thought
:Conkeldurr:
Don't really see it at all tbh. It's incredibly lacking in defensive profile and invites in a lot of dangerous pokemon (Meganium, Floette, Aegislash, Annihilape, Staraptor) and is heavily prediction reliant which is quite undesirable given how slow it is, making wrong predictions very punishing. It's not horrible don't get me wrong, but it's niche at most and I don't really think it goes beyond that.
:Dragalge-Mega:
This one's totally fine. The departure of YChu is actually good for it, since now it's not perpetually pressured to run max spdef and can focus on other spreads and movesets. It still nicely checks Mega Meganium while also beating up Hatterene, is a great Primarina check (though I've never been that high on this mon but hey, it's there), absorbs and sets toxic spikes which in this meta is very valuable, and just has good longevity and is a nice active pivot that doesn't have to fear dropping momentum like some other pivots do.
:Garchomp-Mega-Z:
This mon is very solid and I'm even more high of opinion on this mon than I was when I first nommed it in the VR thread. Strong speed control and wallbreaking in one slot, capable of soft checking a lot of frailer offensive in a pinch. Being spikes immune means it also isn't that easy to wear down, and providing teams with a webs immune speed control option that's this fast is nice. Solidly customizable moveset too. Of course, big opportunity cost when base Chomp is so good, but there's real merit to this mon as well. Don't overlook it, give it a try.
Side note, but... I miss :Mandibuzz:
Kinda wish we had it around right now.