I realise I'm a bit late to the party but I got the chance to jump online for a few hour yesterday so here's my thoughts on the 'suspects' thus far.
Shaymin-S: Ugh, I find it very difficult to motivate myself to play in a metagame where this little shit exists. The list of Pokemon that can a) switch into Seed Flare and b) outspeed or survive the incoming attack after accounting for the SpD drop is ludicrously small. And even then, you need to consider the threat of the SubSeed set. And even if you pack a good counter and scout the set well, there's always the chance the Skymin player will just shrug his shoulders and think 'may as well just try my luck' and flinch you to death. Shaymin-S has no redeeming factors in this metagame, it just makes the whole game notably less enjoyable.
I have to agree. I actually find it similar to Inconsistent. You can beat it easily enough, but then there are those times when it flinches you 8 times in a row (yes that has happened to me) and you die. Then you bring in another pokemon to kill/counter it. It gets 3 consecutive Sp Def drops and kills you. The problem here is that it gets lucky with flinch and stat-lowering, thanks to Serene Grace. The difference between it and Kiss/Rachi is that they have lower attacking stats and speed, which allows it to flinch more and KO more easily. I it should be banned because it can beat anything in the metagame by simply being lucky.
Darkrai: I've came up against surprisingly few Darkrai considering how good it looks on paper. Normally when I do encounter it, it puts something to sleep and damages a Pokemon or two before going down. I''ll need to face a few more of them before I say anything definite.
I don't know about Darkrai. On the one hand, it basically sleeps a pokemon and dies (when I face it, anyway). But in this Gen, sleep is similar to death. With a pokemon that is guaranteed to "kill" something, it's tough to say. Won't sweep a team, but the fact that it shuts down a pokemon no matter what is somewhat disturbing.
Manaphy: Incredibly good Pokemon, both in and out of Rain. It's skating the line between 'top tier OU threat' and 'probably uber' so I wouldn't like to say at the moment. A lot is being made of how threatening it is in Rain, but it should be noted that if you want to use Manaphy in Rain you have to bring Politoed along for the ride too which not only doubles up on weaknesses but forces you to adapt an entirely different playstyle and begs the question 'are Politoed + Manaphy teams really all that?' I never had huge problems with them whilst using my Sandstorm team (granted I had CBTar to Pursuit Politoed hehe). I view Manaphy as the pot of gold at the end of the rainbow for any Rain player that manages to play smartly and win the 'weather-war.'
A lot is being made of Tail Glow's 'OMG +3!' powers but you need to put it into perspective and note that that produces 747 SpA for Timid Manaphy after a boost. Swords Dance Garchomp hits 718 Atk, NP Lucario hits 722, Jolly Doryuuzu hits 738. The +3 isn't the important thing - what's important is the number that you land at after using it and 747 is impressive but it isn't exactly out of proportion with other threats. He isn't that easy to revenge kill to be fair but this metagame is dominated by hard hitting Pokemon with higher than 100 base Spe (Randorosu, Garchomp, Terakion, Latios, Volotoros, Skymin, Deoxys-A) not to mention all the Pokemon that force him into deadly speed ties (Zapdos, Celebi, Shaymin-L). I think we've been a bit quick to condemn Manaphy, I would like to see him given more of a chance.
I think Manaphy should be banned, because there are only two ways to guarantee that you'll beat it. Kill Politoed and set up your own weather, or have all your pokemon able to kill it to avoid having to switch. The former is not plausible because it basically causes you use a pokemon that may not benefit your team at all, simply to beat one pokemon. The latter is not plausible because the pokemon that most benefits your team and will best help your strategy may not fit that description. Manaphy hasn't been any trouble for me personally, but I still believe in a ban for it.
Politoed: I've found Rain to be a lot weaker than Sand, thanks to the fact that Choice Band Tyranitar can come in on Politoed and Pursuit it (72% - 85% vs 252/0) or Stone Edge it (90% - 107% vs the same Toed). Even when I wasn't using Sand, I just randomly slapped Sunny Day on one of my support Pokemon's filler moveslots and forced a tonne of ragequits against opponents who saw that I didn't have Ttar/Hippo/Ninetales/Aboma and thought they could sacrifice Toed. I hated Rain in 4th Gen as much as anybody and was sure that it would be broken as hell in this generation but I'm finding it surprisingly manageable. Still, there has been occassions where I never got momentum in my favor and just got steamrollered but I could say the same thing has happened to me against offensive SS teams or whatever.
Rain is manageable, but it can be tough to handle. I don't necessarily think we should ban rain itself just yet. Let's see how it does as the metagame progresses.
Deoxys-A: Not sure yet, I've had occassions where it absolutely kicked my ass, but I've also had occassions where it got off one resisted attack and then died to priority or Pursuit. Gimme more time on this one.
Although nothing can switch into Deoxys-A, it can really only deal with offensive pokemon. Almost any defensive pokemon can take a hit and KO it. And most teams do have at least one pokemon which can do that already. The only teams I've seen it act broken against were HO teams. I say that Deoxys-A is not broken.
Doryuuzu: A good Pokemon but overated to hell and should never have even been mentioned as a suspect. I find Terakion much more threatening.
I cannot agree more. Good prediction is all it takes to kill Doryuuzu. If you are obviously in a bad position when it comes in, attack. It'll Swords Dance as it predicts your switch, and you'll put it into easy revenge-kill range. If you care in a neutral position when it comes in, then switch out to something to take the hit, then kill it as it attacks or boosts. While this doesn't apply to every situation, a team doesn't have to devote a slot to beating Dory, or use un-viable pokemon. Dory doesn't mean an automatic win when it comes into play. Doryuuzu is good, but is too easily dealt with for a ban, imo. It has to have very specific circumstances to 6-0 a team, which you can prevent from being given to it in the first place. I laugh at the idea of Doryuuzu being broken.