Omastar
Ban. Omastar restricts you to using a Scarfer that has at least 90 base speed or priority that can hit it super effectively, only other way to beat it is with a Water-type of your own and try to bait out Meteor Beam, but I've seen more people starting to run Earth Power so that's not really all that consistent.

Clawitzer 
Ban. Clawitzer is effectively unwallable (unless you want to use Frosmoth or...Marill? lol). While it's pretty slow, it can still in pretty easily on slower and passive mons like Palossand or with U-turn from for example Archeops. It's a little prediction reliant but against a lot of teams you can spam Dragon Pulse or Water Pulse

Kingler 
Ban. Can setup on a good chunk of physical mons and is very hard to outspeed/revenge kill after an Agility. It can kill most things on offense after just a little chip and can tear through balance. Liquidation + Body Slam basically hits everything you need to hit and it's able to adapt to new counters like Guzzlord/Ferroseed with Superpower or Gourgeist-Large/Tangela with Ice Beam.

Ribombee 
Do Not Ban. Ribombee can be overwhelming in matchups where you don't have anything that reliably counter it, but there's enough viable mons that do that. Gigalith, Silvally-Steel and Charizard just to name a few, some of these counters don't have very reliable recovery but there's plenty that do and the ones that don't have good recovery take very little damage from both Moonblast and Psychic. 

Toxicroak 
Do Not Ban. Because almost exclusively Nasty Plot sets get used (mainly to revenge Omastar), I don't think Toxicroak is a big problem. You know what set to expect and it's not that hard to deal with, if/when people are gonna start using other sets I can see it being more problematic for now I think it's a fine addition to the tier.