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