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( Hey, that rhymes! :) )
Things I have changed will be in bold.
Politoad @ Choice Specs
4 HP, 252 SpeAtt, 252 Speed
Modest Nature
Hydro Pump
Ice Beam
HP Grass
Psychic
You can keep your original EV Spread, I just find the extra Speed to be nice.
Looking good!
Psychic helps you deal with Fighting Types.
Hydreigon @ Life Orb
252 SpeAtt, 252 Speed, 4 HP
Timid Nature
Draco Meteor(Dragon Pulse is good, too)
Focus Blast(Superpower on a special set is not the best idea)
Fire Blast(Or Flamethrower)
Tri Attack/Charge Beam
Roost is pointless on Hydreigon, he's only going to survive a max of two hits. Flamethrower is more reliable Fire Blast, choose yourself between Accuracy and Power, and go with Draco Meteor only if you plan on switching him out immediately after to reset his Special Attack.
I noticed that you don't really have a good counter for Water Types, who will be stealing your Rain boost. Charge Beam would be a great move here, as it may raise your Special Attack as a bonus. Tri Attack is an alternative if you want to possibly inflict some status, but personally, I would go with Charge Beam.
Starmie @ Life Orb
252 SpeAtt, 252 Speed, 4 HP
Timid Nature
OR
4 SpeAtt, 200 SpeDef, 52 HP, 252 Def
(I'll edit in the Nature)
Thunder
Hydro Pump(or Surf)
Ice beam
Rapid Spin
The second EV Spread is similar to one I've been using a while, and I think it would benefit this team a lot. It makes Starmie very bulky, and it works better than it may look like it will.
I suggest Thunder over Thunderbolt. Since you have Rain, why not use it?
Toxicroak
Looking really good, nothing to add except that, well..I understand that you'd switch it into a resisted hit, then set up and sweep, but to be honest, I think your opponent will KO you after you use your turn Swords Dancing. Toxicroak is NOT bulky enough to take both hits. If you go with the bulky Starmie set I suggested, you can switch Starmie into hits, and only use Toxicroak when you are sure you can pull it off. If you take my advice here, change the item on him to Focus Sash.
Ferrothorn @ Leftovers(you can go with Rocky Helmet, too, it really kicks butt with Iron Barbs)
252 Def, 248 SpeDef, 8 HP (Note: Consider sacrificing 4 EVs in any of those, and putting them in Attack. It'll help Power Whip a bit, trust me.)
Nature: Relaxed
Power Whip
Leech Seed
Thunder Wave
Stealth Rock
You're pretty close to perfection there. There's no problem if you want to keep Knock Off, Leech Seed is just a really great move, especially on Ferro.
Sableye
Excellent, excellent, nothing to add here. :)