As for Hydration Manaphy, that is a bit more difficult but not invincible by any means. You do realise that if it carries Rain Dance/Rest then it will have only two moves (1 if it carries Tail Glow). These are normally a combination of Surf/Ice Beam/Grass Knot (or Energy Ball). With just Surf, IB or Surf and Ice Beam, basically every water pokemon resists it. If it is IB/(Grass Move), then every Steel Type resists it. And finally, if it is Surf/(Grass Move), any Dragon or Grass type will wall it with ease. The thing is, whilst Rain Dance Manaphy might be a bitch to kill, it suffers from moveslot syndrome, and so it can inevitably sit there and do nothing. Gyarados can own any non Tail Glow version with Taunt + Dragon Dance. Metagross and Garchomp can also set up on it, which can spell doom for your team. Having said that, there are probably some arguments that are in favour of it being uber, but when it comes down to it, I believe that it at least deserves a chance in OU before being banished to Ubers.