Omastar: Ban.

It forces you to run a scarfer with 90+ speed or vaccum wave/mach punch, and even then you can lose if you send your scarf togedemaru on a hydropump for instance. I believe the best scarfers are passimian and mesprit and togedemaru, so basically it comes down to using toxicroak with vaccum and/or scarf toge in every team. Else you rely on terrible mindgames around meteorbeam with your lanturn or guzzlord, which cant handle +3 meteor beam even with an assault vest. Omastar limits teambuilding and is just unhealthy overall.
Kingler: Ban.

Vaporeon leaving just enabled Kingler to spam Liquidation and tear teams apart. Knock off and BodySlam give it perfect coverage, since Knock off oneshots would be checks like Gourgeist (offensive gourgeist) and Bodyslam does an awful lot to Whimsicott, Toxicroak and Lanturn. The last move that makes it definitely broken is agility, since it can setup easily on any physical attacker like Passimian, Regirock or even togedemaru, and then proceed to outspeed everything and OHKO almost everything that has been weakened a bit or not, while being sort of immune to accelerock or machpunch that barely damage it.
Clawitzer: DnB.
I'm probably wrong but I find clawitzer scarier on paper than in practice. Not only does it lack Kingler's Physical bulk and access to agility, but Clawitzer also suffers from being locked into a move, which makes it more prediction-reliant even tho Darkpulse is quite free. Common mons like lanturn, whimsicott, toxicroak and guzzlord can stop clawitzer's momentum. By resisting one or two attacks. Clawitzer is also very slow, and doesnt have great bulk, so it isnt that easy to make it work imo. Definitely a mon to watch out for.
Toxicroak: DnB.
Difficult mon to switch into especially when your rocker is regirock. However that's pretty much the only thing it can setup on, and it isnt too hard to pressure croak, with anything faster or bulky mons like sandaconda, garbodor and gigalith (depending on the set). The only thing that could push it over the edge is that u never know if it's physical or special croak, but I dont feel like it's too much right now, and I really appreciate how it functions as a glue to absorb scalds, remove toxicspikes, check omastar, and be a wallbreaker that isn't (too) weak to passimian. 
Ribombee: DnB.
Strange mon, since it feels like it's bad or great at the same time. In practice it's difficult to use it in teams because whimsicott just has far greater utility and typing. But bee is extremely fast and strong, and a choice specs set is impossible to switch into unless you have a specially defensive steel-type. Fortunately it is weak to stealth rock. However Quiver dance + Boots sets can be destructive late game, and I wouldnt say weakening its checks is too hard: it's just something you will only do if building Around bee, and most of the time you wont bee beelding around bee.