Some prior discussion of these Pokemon took place here, posting on behalf of myself and not the BW tiering council
Cloyster and Volcarona have been among the most controversial Pokemon in BW OU for a while now. Over the last few months, I have received a (large) handful of complaints about both and I experience some difficulties with them as well, so I think it is a good time to discuss these Pokemon. I am not personally firm on anything happening before the upcoming SPL (although not opposed -- some others have been quite outspoken about wanting action and that's part of why I am posting this), which starts in about 6 weeks, but I do think beginning discussion and seeing where support lies is for the best. I underline this as this is not a request for an immediate ban or suspect of any kind, but rather just trying to get discussions going to see what players think and feel. I will also relay information from this thread to the BW council chat as we have not had much to discuss for some months now.
One additional note here is that both Pokemon have been at the center of other tiering action with Cloyster being involved with King's Rock and Gems being banned while Volcarona was also involved with the ban of Gems. Normally we like to focus on the Pokemon first and keeping our banlists focused on Pokemon barring exceptional circumstances, but some outlier circumstances such as an uncompetitive, RNG focused item like King's Rock and a set of items that was a common thread in problems like Gems put us in an interesting position of trying to see how balanced things would become. At a certain point, however, a lot of people believe we should begin to look at the Pokemon themselves. So let's do that!

Cloyster has been one of the best set-up options in BW for a couple of years now, coming to prominence and a peak well after the generation's end. Initially it was used primarily as a cheesy win condition with King's Rock, puttng it one flinch away from getting extra kills often and a couple flinches away from potentially sweeping even the most prepared opponents outright. This got banned, so Cloyster pivoted to using Ice Gem and eventually Rock Gem thanks to the rise in gems being used with multi-hit moves. These gems allowed Cloyster to circument most common counterplay if it could get a Shell Smash off cleanly, which was one of the numerous contributing factors to the aformentioned gems ban.
Since then, Cloyster has maintained its place as a strong option in the metagame. Never-Melt Ice variants took over first as they allowed Cloyster to OHKO specially defensive Ferrothorn, Scarf Latios (Ice Shard), Tyranitar, Reuniclus, Gastrodon, Seismitoad, and others at +2. Soon thereafter dice and some others started to frequent Lum Berry, which allowed for Cloyster to mitigate the threat of Toxic from Gliscor, Bronzong (the first time), Excadrill, Politoed, Tentacruel, and others while eliminating burns from various Scald users Will-O-Wisp Jellicent. We have even seen niche options on Cloyster like Focus Sash when paired with Aerodactyl or Terrakion leads, normal moves like Spike Cannon or Double Edge with boosting items to potentially dispose of would-be checks like slightly chipped Keldeo, and various other fringe options. The underlying point is that a lot of the things older Cloyster did that made it problematic -- which was mainly being able to pick its own counterplay within the scheme of offenses -- Cloyster is beginning to do regardless. We have begun seeing Bronzong or Shadow Ball Jellicent as saving graces on balance teams frequently and offenses feel more of a need to fit one of Jirachi or Scizor if they cannot fit Magnezone, which conveniently covers the vast majority of Cloyster variants, than ever before. This makes Cloyster still plenty playable within the metagame, but quite restrictive overall in a metagame that cannot really afford that always.

Volcarona is a Pokemon we all know about: it is an annoying, dynamic sweeper with potential to snowball out of control and potential to dampen the mood on teambuilding. It adds quite a bit to the tier as it helps expand the scope of match-up coverage and pressure for offenses, but it ultimately is doing the same things now as it has done for many years, including when it drew the ire of players when it contributed to gems being banned.
The main functuonal difference is that Volcarona does not blow up Tyranitar at +1 after Stealth Rock with Bug Gem Bug Buzz now, which means variants with Rock Slide (or Crunch after chip/Thunder Wave if it is not Lum) can essentially trade with Volcarona, which tends to be a good trade as Tyranitar is not needed for the normal onsalught of physical sweepers we see alongside Volcarona on conventional offenses. Sure, things like Psychic Gem can be clutch for Tentacruel, but Lum Berry and the right coverage does a lot of the same things in the long haul while covering for other match-ups, too. The great Volcarona debate, unfortunately, is due for another chapter given all of this. I do find it contained a bit more possibly than Cloyster due to not being able to circumvent certain counterplay as it cannot bypass Sash from Alakazam or certain faster Scarf users as it lacks priority while Cloyster does not mind either of these, but Volcarona still is an incredibly cheesy Pokemon that requires a lot of strain on teambuilding and potential guesswork within the game to derive an optimal line of play to defeat it without losing the wrong things.
I hope those that are active and current in BW OU's metagame comment!
Cloyster and Volcarona have been among the most controversial Pokemon in BW OU for a while now. Over the last few months, I have received a (large) handful of complaints about both and I experience some difficulties with them as well, so I think it is a good time to discuss these Pokemon. I am not personally firm on anything happening before the upcoming SPL (although not opposed -- some others have been quite outspoken about wanting action and that's part of why I am posting this), which starts in about 6 weeks, but I do think beginning discussion and seeing where support lies is for the best. I underline this as this is not a request for an immediate ban or suspect of any kind, but rather just trying to get discussions going to see what players think and feel. I will also relay information from this thread to the BW council chat as we have not had much to discuss for some months now.
One additional note here is that both Pokemon have been at the center of other tiering action with Cloyster being involved with King's Rock and Gems being banned while Volcarona was also involved with the ban of Gems. Normally we like to focus on the Pokemon first and keeping our banlists focused on Pokemon barring exceptional circumstances, but some outlier circumstances such as an uncompetitive, RNG focused item like King's Rock and a set of items that was a common thread in problems like Gems put us in an interesting position of trying to see how balanced things would become. At a certain point, however, a lot of people believe we should begin to look at the Pokemon themselves. So let's do that!

Cloyster has been one of the best set-up options in BW for a couple of years now, coming to prominence and a peak well after the generation's end. Initially it was used primarily as a cheesy win condition with King's Rock, puttng it one flinch away from getting extra kills often and a couple flinches away from potentially sweeping even the most prepared opponents outright. This got banned, so Cloyster pivoted to using Ice Gem and eventually Rock Gem thanks to the rise in gems being used with multi-hit moves. These gems allowed Cloyster to circument most common counterplay if it could get a Shell Smash off cleanly, which was one of the numerous contributing factors to the aformentioned gems ban.
Since then, Cloyster has maintained its place as a strong option in the metagame. Never-Melt Ice variants took over first as they allowed Cloyster to OHKO specially defensive Ferrothorn, Scarf Latios (Ice Shard), Tyranitar, Reuniclus, Gastrodon, Seismitoad, and others at +2. Soon thereafter dice and some others started to frequent Lum Berry, which allowed for Cloyster to mitigate the threat of Toxic from Gliscor, Bronzong (the first time), Excadrill, Politoed, Tentacruel, and others while eliminating burns from various Scald users Will-O-Wisp Jellicent. We have even seen niche options on Cloyster like Focus Sash when paired with Aerodactyl or Terrakion leads, normal moves like Spike Cannon or Double Edge with boosting items to potentially dispose of would-be checks like slightly chipped Keldeo, and various other fringe options. The underlying point is that a lot of the things older Cloyster did that made it problematic -- which was mainly being able to pick its own counterplay within the scheme of offenses -- Cloyster is beginning to do regardless. We have begun seeing Bronzong or Shadow Ball Jellicent as saving graces on balance teams frequently and offenses feel more of a need to fit one of Jirachi or Scizor if they cannot fit Magnezone, which conveniently covers the vast majority of Cloyster variants, than ever before. This makes Cloyster still plenty playable within the metagame, but quite restrictive overall in a metagame that cannot really afford that always.

Volcarona is a Pokemon we all know about: it is an annoying, dynamic sweeper with potential to snowball out of control and potential to dampen the mood on teambuilding. It adds quite a bit to the tier as it helps expand the scope of match-up coverage and pressure for offenses, but it ultimately is doing the same things now as it has done for many years, including when it drew the ire of players when it contributed to gems being banned.
The main functuonal difference is that Volcarona does not blow up Tyranitar at +1 after Stealth Rock with Bug Gem Bug Buzz now, which means variants with Rock Slide (or Crunch after chip/Thunder Wave if it is not Lum) can essentially trade with Volcarona, which tends to be a good trade as Tyranitar is not needed for the normal onsalught of physical sweepers we see alongside Volcarona on conventional offenses. Sure, things like Psychic Gem can be clutch for Tentacruel, but Lum Berry and the right coverage does a lot of the same things in the long haul while covering for other match-ups, too. The great Volcarona debate, unfortunately, is due for another chapter given all of this. I do find it contained a bit more possibly than Cloyster due to not being able to circumvent certain counterplay as it cannot bypass Sash from Alakazam or certain faster Scarf users as it lacks priority while Cloyster does not mind either of these, but Volcarona still is an incredibly cheesy Pokemon that requires a lot of strain on teambuilding and potential guesswork within the game to derive an optimal line of play to defeat it without losing the wrong things.
I hope those that are active and current in BW OU's metagame comment!