....well i guess the hail discussion has died down a bit (although some more discussion on its status in the tier would be cool). So i guess i'll post about something different for now :).
Regenerator Cores
With many great defensive Pokemon possessing the ability, including Slowking, what is arguably the best Pokemon in the tier, Regenerator cores have been quite commonplace in RU for a while now. Of course, Slowking+Tangrowth and the like aren't nearly as hard to break as they were in BW1, but they're still effective defensive cores capable of taking on much of the tier, especially when supported to cover their flaws common Regenerator cores these days include Slowking+Tangrowth, Slowking+Amoonguss, and Alomomola+Amoonguss. So first off, lets look at Regenerator. Regenerator is probably one of the best abilities in Pokemon at the moment, granting the Pokemon with the ability essentially free recovery every time they switch in and out. This makes Regenerator one of the best abilities for a defensive Pokemon or bulky pivot to have. As for the Pokemon themselves, all of the Regenerator Pokemon in RU possess high defensive stats, multiple important support moves such as Spore, Thunder Wave, Stun Spore, Sleep Powder, Toxic, Wish, Heal Bell, and Clear Smog, and have excellent type synergy to boot! Further augmenting the usefulness of these cores. Now Regenerator cores are usually seen as defensive, but what people always seem to forget is that Regenerator is a great ability for an offensive Pokemon too, letting them heal off potential residual damage from attacking and last longer throughout the match. Specs Slowking, Offensive Trick Room Slowking, Offensive Tangrowth, and Life Orb Amoonguss are good examples of good offensive Regenerator Pokemon. Now as i mentioned before, Regenerator cores are common and powerful, but they're far from unbreakable, especially in the current metagame. Here are a few examples of things that break regenerator cores/make them easier to handle.
Substitute+Bulk Up Braviary
Substitute+Bulk Up Braviary is perhaps one of the best ways to break through defensive varients of these Regenerator cores. Although Braviary is usually seen as sort of a glass cannon because of its Stealth Rock weakness and the recoil damage its taking from Brave Bird, Braviary actually has decent 100/75/75 defenses, allowing it to be eved so that none of the common Regenerator Pokemon can break Braviary's sub in one hit. From there Braviary can simply repeatedly set up with Bulk Up, using Roost to heal off any damage taken during the process, and smash through the poor core when its ready to sweep. Not even Alomomola is bulky enough to take repeated Brave Birds from a boosted Bulk Up Braviary!.
Lum SD Gallade
Lum Swords Dance Gallade is also a good check to regenerator cores. SD Lum Gallade has the ability to set up a Swords Dance against any attack a regenerator core would be able to throw at it bar maybe Tangrowth's Power Whip, and its trusty Lum Berry makes sure the core can't attempt to cripple Tangrowth with status. Once set up, Gallade can just power through the core with a combination of Close Combat, Zen Headbutt, and Leaf Blade. Not even Alomomola and Tangrowth can take on a boosted Gallade (unless the latter has Power Whip). As Gallade can simply grab an extra boost and smash both of them with a +4 Close Combat, which astoundingly OHKOs both of them. Lastly, Gallade is incredbly good at breaking down defensive cores in general, so other Pokemon that might be used to cover a Regenerator core's weaknesses might not be able to beat Gallade after a boost.
Hazards overload
While Regenerator Pokemon are a bit more resistant to Entry hazards compared to other Pokemon thanks to their passive recovery, large amounts of entry hazards can still wear them down, counteracting Regenerator and making the core much harder to break through. Qwilfish, Ferroseed, Crustle, Smeargle, Steelix, Omastar, Uxie, and Druddigon are good examples of common hazard setters, and Ghost-types such as bulky Rotom, Misdreavus, and Spiritomb are good options to counteract any attempt to spin these hazards away.
Escavalier
Escavalier can be quite tough for any Regenerator core to handle, especially with a bit of Speed Creep to outrun Slowking, Amoonguss and the like. One of the major flaws of the TanKing Regenerator core way back then was that it lacked a way to take on powerful Bug-type Pokemon, and Escavalier is no exception. Because of Escav's Bug/Steel typing and good bulk it should be able to switch in on anything except for Slowking's Fire Blast and Amoonguss/Tangrowth's Hidden Power Fire reliably, and can then proceed to smash a team member with its mighty Choice Band Megahorn. Not even Alomomola can stand up to this brute, with Megahorn scoring a guarenteed 2HKO on it after Stealth Rock, even with protect recovery factored in!
SubCM Uxie
SubCM Uxie is in a similar boat to Braviary regarding defensive Regenerator cores, and while it doesn't have any recovery outside of Leftovers like Brav does, Uxie still does a fine job of boosting up and breaking through those cores with ease thanks to its superior bulk, lack of a Stealth Rock weakness, and better overall coverage between Psyshock and Thunderbolt. Once Uxie switches in safely against a Regenerator core, its essentially game over unless the opponent has another method of taking out the pixie, as Uxie can just set up all over them while healing off all the Hp it lost from using Substitute with Leftovers. Out of all the possible regenerator Pokemon, Power Whip Tangrowth probably performs best against SubCM uxie, but can still lose if the uxie user decides to use Psychic (this isn't recommended though!).
So what kinds of experiences have you had with Regenerator cores? Or really Pokemon with Regenerator in general, what teams do you use them on? What kind of support do you give them to cover their weaknesses? and what strategies do you use to break through them?