Alright, so after a couple of battles in this metagame, I think it would be really fun after a bit of work is done. This post will be about the mons(/moves) I think to be the most centralizing or broken right now, then I will talk about mons I think are very good, but not ban-worthy in the slightest. (This is just an overview of their roles, really, but I think it is fun. :x)
Shell Smash: This group has 3 users, and all 3 of these users are all equally deadly and very centralizing. I also believe the attempt to salvage Shell Smash by banning the single-most broken user of the move was a good attempt, but due to the move as a whole being extremely potent and overpowered, it didn't help all that much. (Free Omanyte and get rid of Shell Smash as a whole imo!)
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Clamperl: Clamperl hits an insane amount of SpA with Deepsea Tooth, and adding Shell Smash to this equation just makes Clamperl even more deadly. Shell Smash boosts an already insane amount of SpA and alleviates Clamperl's mediocre Speed problems, allowing it to easily sweep through teams. The only switchins for Clamperl I've found as of late are defensive Snover and Slowpoke.
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Shellder: Shellder has great bulk in this metagame, which allows it to forego Eviolite for my personal favorite on this mon: King's Rock. King's Rock makes an already annoying strategy even more annoying by granting Shellder a 50% chance to flinch its target if it uses a multi-hit move, thanks to Skill Link. Aside from these great coverage moves, Shellder also has priority in Ice Shard if you feel you don't need your Water-type STAB of Razor Shell.
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Binacle: The last, least used, and often forgotten member of our trio. Due to its extremely low use, most of this section will be that of theorymon. However, it has great STABs of Stone Edge and Razor Shell, the latter being boosted by Tough Claws, as well as other Tough Claws-boosted like Cross Chop and Poison Jab. On top of these, its interesting movepool also has Switcheroo which allows it to dump a Choice Band on a wall like Slowpoke or Hippopotas, making these targets much more easily disposed of due to their now lacking Eviolite. Binacle's typing also allows it to potentially have more opportunities to set up a Shell Smash than the former two, as it can come in on Normal- and Flying-types due to it resisting their STABs. This also makes it a decent check to bird spam.
Doduo: Doduo is probably the most broken on in the metagame, barring those with Shell Smash. Doduo has an incredible offensive prowess on par with no other, 18 Speed which is a God-send,amazing STABs in Brave Bird and Return, and Knock Off allowing it to remove Eviolites to let itself wallbreak much more easily, and this also helps out its Shell Smashing teammates of Shellder and Clamperl. While many think that it will likely just end up killing itself, this usually doesn't occur until after it has done what it needs to allow Shellder or Clamperl sweep and finish the match. This thought is also a testament as to how deadly Doduo truly is.
Gothita: Gothita's ability to trap and ill any targets of choosing makes it easily one of the most broken mons in the metagame. This is highlighted even more so due to the only decent Pursuit Trapper being Stunky, and its SpA stat being pretty decent by LC UU standards. With ORAS tutors, it can now run Trick while having Shadow Tag as an ability, meaning it can wallbreak as well as revenge kill.
Now onto those that are good, but not quite on a ban-worthy level:
Pancham: ORAS gave Pancham an extraordinary amount of toys to play with, including new STABs of Drain Punch and Superpower, and coverage options including Knock Off, Zen Headbutt, Gunk Shot, the Elemental Punches, and many other moves. Pancham is a great pivot due to it hitting great bulk of 25/14/12 while maintaining a strong 18 Atk stat and having the move Parting Shot, which also allows Shell Smashers to set up much more easily. It can also run a decent wallbreaking set that foregoes the use of Parting Shot in order to set up Swords Dance, which hits great bulk of 23/14/12, but also hits 13 Spe and 18 Atk. This set means it hits a good benchmark Speed-wise, and has a 36 Atk stat after a single Sword Dance. However, this Speed stat is still quite slow, meaning it is easily revenge killed by the likes of Doduo, Taillow, Elekid, and many others. However, this cute little panda can be a huge threat for defensively oriented teams to face.
Pumpkaboo: With the addition of Synthesis from ORAS tutors, we now have both an incredible wall and amazing spinblocker in the tier. It hits 25/16/14 defensive stats, and has Will-O-Wisp to support the team further, and has offensive options like Bullet Seed, which has incredible rolls in LC, Shadow Sneak, and Rock Slide. The latter is a neat option for Pumpkaboo because it can hit Flying-types like Doduo and Taillow on the switch as the expect to sponge a Bullet Seed or Shadow Sneak. This little pumpkin has proven to be a decent check toShell Smashers, as well, as it lives Shellder's Icicle Spear, if I am not mistaken.
Skrelp: With Adaptability now available, we've gained yet another wallbreaker. It has a great movepool that includes Scald, Hydro Pump, Sludge Bomb, Sludge Wave, Thunderbolt, Icy Wind, and even Dragon Pulse specially, as well as Aqua Tail, Waterfall, Gunk Shot, and Play Rough physically. It also has support options including Haze, Toxic Spikes, and Icy Wind. It also has a great typing which allows it to check every Shell Smasher, Pancham, Riolu, and many other offensive pokemon.
Hype:
Stunky: Probably the best answer to Gothita in LC UU, and Stunky is also the only good Pursuit Trapper we have. It has a good typing, good movepool, and incredible Speed. Its movepool consists of options like Fire Blast (or Flamethrower), Sucker Punch, Play Rough, Sludge Bomb Taunt, Pursuit, Explosion, Memento, and Haze. Due to these assorted moves, it is easy for Stunky to fit onto your team and fulfill roles other than expunging Gothita issues.