I pretty much entirely disagree with Cloyster in A. Keldeo and Technician Breloom running amok are not doing it any favors, making it harder to sweep. Cloyster might have high Defense to set up on some Physical attacks, but that's offset by its low HP. That, and physical Fighting-types are literally fucking everywhere. Regardless, powerful STAB physical attacks can still 2HKO Cloyster or even OHKO it with Stealth Rock. For example, Choice Band Haxorus has a 25% chance to OHKO without Stealth Rock and always OHKOes with Stealth Rock. Ain't setting up on that. CB Kyurem-B's Outrage does 98% minimum, and Fusion Bolt always OHKOes. Not setting up on that either. Granted, these are some of the most powerful attacks in OU, but similarly powerful attacks are still dealing a fuck ton of damage to Cloyster, and these powerful attacks aren't exactly uncommon. Then there's the point when it does set up on a physical attack it can set up on. You're going to have to put up with either piss-poor bulk on both ends (making it easier to revenge with priority, which is everywhere) if you run Life Orb or decidedly poor damage output if you run White Herb. Cloyster is fine where it is.
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