Gyarados is one of my favorite pokes, and it saddens me to see him like that. It is far too weak offensively, and far too fragile defensively, with that set. Either go for that standard BulkyDos set
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Nature:Adamant
212 HP, 16 Atk, 180 Def, 100 Spd
WATERFALL/Ice Fang
Stone Edge/Earthquake
Taunt
Dragon Dance
This allows you to switch into many threats, charge up, and cause pain. You can afford so little EVs in attack, BTW. Taunt is crucial for charging.
Or
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Nature:Adamant
72 HP, 252 Atk, 184 Spe
Dragon Dance
Waterfall
Earthquake/Bite
Ice Fang/Stone Edge
Just pure power, while still charging up.
The standard MixPert is far superior to that.
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Nature:RELAXED
240 HP, 216 Def, 52 SpA
Hydro Pump
Ice Beam
Earthquake
Roar
All about damage, and these moves damages who it needs to hit better. Ice Beam does more to dragons than Ice Punch will ever do. And Earthquake causes pain without EVs in Atk.
I don't know WHY I'm not using it...