Looks like you're going the bulky route. That could work...or work against you. The field will be littered with threats like [email protected]
If you wanna go bulky weather setter, then Hippowdon's your pokemon. It'll give Trick Room setters a reason to hesitate because the Hippo's so slow. Move those defensive EVs to attack. Hippowdon's special defense is so crappy that EVs invested in it won't help whatsoever and its defense is already high. If you want something faster, you can try using Tyranitar.
Brave Tyranitar w/ Sand Stream
Item: Chople Berry / Focus Sash
IV: 0 Speed
EVs: 252 HP / 252 Atk / 4 SpD
~ Rock Slide
~ Low Kick
Standard Tyranitar is standard. If you don't like Low Kick, feel free to switch it with something else. The speed IV should be 0, because it's the slower pokemon that sets the weather.
Murkrow's defenses are crap. Don't be too surprised if it gets KO'ed right after it uses a non-attacking ability. Change Roost to Taunt. It likely won't get a chance to use Roost because it'll die in 1 hit. If you want something that'll survive longer but still use Prankster, try using Tornadus or Thundurus.
Timid Thundurus w/ Prankster
Item: Charti Berry / Yache Berry / Electric Gem
EVs: 4 HP / 252 SpA / 252 Spe
~ Hidden Power Flying / Hidden Power Ice
~ Thunder Wave
~ Substitute / Protect
Change Stoutland's Superpower to Wild Charge. You don't want Stoutland's stats to go down and there's a great deal of electric-weak pokemon around. EVs look good. Try testing Stoutland with Life Orb or Choice Scarf and see which of the three is best suited to your team.
Drop Zen Headbutt on Metagross in favor of Earthquake or Explosion. If you chose Earthquake, give Metagross a Life Orb or Occa Berry. If you choose Explosion, you should consider a Normal Gem. Move the SpD EVs to attack. Metagross needs that power and you're seriously shorting it.
Gastrodon wants all its EVs pumped into HP and SpA so it can tank the most effectively. If you don't mind a power drop and want more bulk, change nature to Bold. Otherwise, looks good.
Cradily there...yeah, no. Gastrodon there can take care of both Politoed and Ninetales. You have cover for Abomasnow in Stoutland and Metagross. Metagross especially. Exchange it for something else. Since most of your pokemon are very slow, you can benefit from using Cresselia if you want to use Trick Room. Even if you don't, Cresselia will be able to absorb special attacks and support your team.
Calm Cresselia w/ Levitate
Item: Sitrus Berry / Chesto Berry
EVs: 252 HP / 4 Def / 252 SpD
~ Icy Wind / Thunder Wave
~ Light Screen / Reflect
~ Helping Hand / Rest
Which one you use depends on your own preference.