Pokemon Black

I know that you guys are so busy with Gen VI games right now so feel free to ignore this thread of mine although those who will answer will be highly appreciated.

So, basically, I just need suggestions or corrections, etc about my current team. Me and my brother will have a little fun battle next week and I'm not really planning to lose so, here goes.

Samurott (EV trained in ATK and SPD)
-Ice beam
-Waterfall
-Sword Dance
-X-Scissor (For grass types)

Darmanitan (EV trained in ATK and SPD)
Ability : Sheer Force
-Flare Blitz
-Hammer Arm
-Thrash
-U-turn (In case a water pokemon shows up. I'm honestly planning to replace this)

Hydreigon (EV trained in SP. ATK and SPD)
-Dragon Pulse
-Flamethrower
-Draco Meteor
-Thunder Wave

Metagross (EV trained in HP and SP. DEF)
-Bullet Punch
-Zen Headbutt
-Meteor Mash
-Iron Defense (I'm willing to replace this with Agility)

Galvantula (Ev trained in SP. ATK and SPD)
Ability : Compound eyes
-Thunder
-Bug Buzz
-Volt Switch
-Thunder Wave

Tornadus (EV trained in ATK and SPD)
-Acrobatics
-Crunch
-Hammer Arm
-Tailwind

Thanks.
PS. I'm still playing Pokemon Black because our Nintendo New 3DS is scheduled for next month... according to my mom and I'm so excited already!

Giving natures for each of your Pokemon would be highly appreciated.

Ice Beam is useless on Swords Dance Samurott. As an FYI, it also hits Grass Pokemon.

Samurott is better off going physical only or a specially-based mix:
-Hydro Pump
-Ice Beam
-Grass Knot/Aqua Jet
-Taunt/Superpower/Megahorn
Nature: Modest/Rash/Naive
EVs: 4 Def/252 SAtk/252 Spe or 84 Atk/180 SAtk/244 Spe
Item: Life Orb

or
-Swords Dance
-Waterfall
-Megahorn
-Aqua Jet
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry/Splash Plate/Mystic Water

Darmanitan has no use for Thrash; it has poor coverage. Hammer Arm also wastes away Darmanitan's decent Speed. A resisted Sheer Force Flare Blitz still outdamages a neutral U-turn:

252 Atk Sheer Force Darmanitan Flare Blitz vs. 0 HP / 4 Def Samurott: 153-180 (46.2 - 54.3%) -- 57.8% chance to 2HKO

252 Atk Darmanitan U-turn vs. 0 HP / 4 Def Samurott: 92-109 (27.7 - 32.9%) -- guaranteed 4HKO

-Flare Blitz
-U-turn
-Rock Slide
-Earthquake/Superpower
Nature: Adamant/Jolly
EVs: 252 Atk/4 SDef/252 Spe
Item: Life Orb/Choice Band/Choice Scarf
Ability: Sheer Force

Hydreigon's movepool is very good, and you're not taking advantage of that:
-Draco Meteor
-Focus Blast
-Fire Blast/Flamethrower
-Dark Pulse/U-turn
Nature: Modest
EVs: 4 HP/252 SAtk/252 Spe
Item: Choice Specs

or
-Substiute
-Dragon Pulse
-Focus Blast
-Fire Blast/Roost
Nature: Modest
EVs: 4 HP/252 SAtk/252 Spe
Item: Leftovers/Life Orb

or
-Dark Pulse
-Flamethrower/Draco Meteor
-Focus Blast/Draco Meteor
-Roost
Nature: Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb

Agility is always the preferred boosting move on Metagross; Iron Defense isn't worth it, as it could make Metagross a critical hit magnet:
-Agility
-Meteor Mash/Ice Punch
-Zen Headbutt
-Earthquake
Nature: Jolly
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Ability: Clear Body

Thunder Wave isn't that useful on Galvantula, as it's already very fast. Hidden Power (Fire) is preferred on it to hit Steel Pokemon hard, especially Scizor. But if you can't do that, use Giga Drain or Energy Ball over it, to hit Ground Pokemon.

Physical Tornadus should have a Flying Gem attached. Hammer Arm wastes away its good Speed:
-Acrobatics
-Superpower
-Taunt/Bulk Up
-Tailwind/Taunt/Substitute
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Flying Gem
Ability: Prankster