Terrakion
Terrakion truly is a beast, I don't mave much to say about this. Though, some other sets you might like are: Swords Dance, Subdance, and Double Dancer. Oh, and a scarf. Not that your set isn't good. But those are some options for you.
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Hydreigon
I see that you need a good fast scarfer,since you need some late game sweepers to wipe up the board. Expert Belt is good, obviously, but Hydreigon's good movepool make it a good Pokemon to just come in and finish someone off. It's big variety of moves lets it come in and choose a move at will, and just use it. Just a though. Oh, Thunderus-T might work as a scarfer, too. Another choice to consider.
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Confagrigus
Why the Confagrigus? I honestly don't see a point for this guy on your team. If you want Will-O-Wisp there are plenty of choices out there, there are also many fighting and normal resist pokemon out there, for example Gengar screws them and so does Sableye. (With Will-O-Wisp) So I wouls suggest replacing this with Gengar, since I don't know what your doing I'll just put another ghost. Gengar can be aminly used two different ways, SubDisable or Special Attacker. Sub Disable uses Gengar's fast speed to pair it up with Disable, redering one opponent's move useless. Life Orb attakcer Gengar uses it's high SpA to attack, and most of the time getting back HP with Giga Drain.
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Jirachi
Hello random EVs? What's with you're EVs, they look messy. 80 HP / 252 Atk / 176 Spe <- Try that. Try replacing Wish for Sub. And whats with the Stealth Rock? You have it on Ferrothron...? Replace it for another move or have Sub + Wish.
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Ferrothron
Just to point out that Spikes can be helpful for this team. Other than that, no comment.
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Gyarados
I don't see a point in Water Gem. You already have STAB. Dragon dance boosts your attack to ridiculous levels. But don't' take my word for it, I usually see no point in using gems other than for Acrobatics xD This is also good, but maybe have Sub somewhere? Not vital, just a thought.
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Other than those little suggestions, this team is looking solid. Great job! Good luck with the team.
