I really don't want to vote for Poison Heal Goodra. Not because I think it'll be OP, which it won't be, but because it's yet another Poison Heal suggestion. I can appeciate the ability, but I'm a little sick of seeing it. I think Poison Heal Snorlax made me sick of seeing the ability, to be honest. This is a good idea, but I think we need to take a break from defensive Poison Heal suggestions. I'll avoid talking about it any further, anyways.
But I didn't come here just to bash Goodra, as I have a few things to say about the other theorymons. Water Shuriken Cloyster is alright, and it's certainly a buff, given the extra priority it gets to get the jump on weakened foes without needing to set up Shell Smash, but I wouldn't say it's a significant buff, since base 95 attack only deals so much damage from a base 75 attack, even with STAB. He really needs the Shell Smash boost to deal large amounts of damage with it, and since it doubles your speed, it really defeats the purpose of using its priority unless you're scared to death of Talonflame, and you'd be better off using Razor Shell if you ask me.
Refrigerate Avalugg is a decent idea, and I think is worth testing out anyways. With Rapid Spin as an Ice-type move, nothing can block it and prevent hazards from being spun away, which is always neat. Plus, he can actually take physical hits better than Hippowdon, which is a great asset to have in my book, and being able to hit hard with Refrigerate Return is an excellent bonus. But lacking any weaknesses aside from Ice and having 4 rather crippling weaknesses really lets him down, and having base 46 special defense makes him easy prey for special attackers, but he at least has Sturdy to survive a hit and do his job at least once. Being vulnerable to all forms of entry hazards and having a Stealth Rock weakness does no favors for him, especially since his role is switching into and spinning away hazards. Not the best idea, but far from the worst.
And finally, we have Snow Warning Kyurem. This is a mix of good and bad; on the good side, base 130 special attack and STAB 110 attack in Blizzard are amazing to have, and having base 95 speed is also good for wallbreaking. His equally good base 130 attack shouldn't be overlooked, so he can hit special walls harder. But that's really it. In terms of consistent weather summoners in OU, Mega Charizard Y can easily 2HKO with Fire Blast, whether it's in the sun or hail, and (Mega) Tyranitar has to be cautious of Focus Blast if sand isn't up, but there aren't any problems aside from that, though Specs sets can KO even with sand up. In terms of special sweeping, base 95 speed only goes so far, and there are a plethora of speedsters that can take him on. His bulk is excellent, and does have Roost to keep himself alive, but like Avalugg, he's vulnerable to every hazard and weak to Stealth Rock, not to mention that he has a terrible defensive typing leaving him with 5 exploitable weaknesses. This will likely get my vote, but I'm none too impressed with this one.