This thing is absolutely ridiculous. What can even counter this thing with any kind of effectiveness? Bulky waters are 2HKOed before they can 2HKO back. Skarmory is 2HKOed and can't kill it. Mach punch coming from technician-top and roobushin is also only a 2HKO and even 252/0 roobushin is likely to be OHKOed by +2 icicle spear.
The only thing in OU that can do something to it is Nattorei but it still dies if it's not at really high HP. I'm surprised I don't see more cloysters. If it manages to come in after something dies and set up a shell break, nothing can really stop it from taking down at least 1 of your pokemon. You would more than likely have to sacrifice a huge chunk of your physical wall's HP to kill it which then leaves your team open to further physical sweepers.
The only thing in OU that can do something to it is Nattorei but it still dies if it's not at really high HP. I'm surprised I don't see more cloysters. If it manages to come in after something dies and set up a shell break, nothing can really stop it from taking down at least 1 of your pokemon. You would more than likely have to sacrifice a huge chunk of your physical wall's HP to kill it which then leaves your team open to further physical sweepers.