Gen 8 Flygon guide
A repost of an original Flygon set I made when answering a question about Dragons in Gen 8. It seemed to get lots of good feedback on that thread so I'll share it here.
Flygon @ Expert Belt / Blunder Policy* / Life Orb
EVs: 252 Atk / 4 SpD / 252 Spe
- Dragon Dance
- Superpower / Stone Edge
- coverage move (Fire Punch, First Impression, Dragon Rush if you're real brave)
Now there is definitely a reason Flygon wasn't put in OU, and I'm sure that reason is because it's not as good as other Dragon-type options, but it's still plenty capable of holding its own. I had a bit of a tough time thinking of the proper item for it. I almost Life Orbed it, but I'm not so sure I want a DDancer with an even further limited health pool. It's usable in OU, but can be a little bit of a risk if you don't know exactly what its problems are.
Flygon is kind of strange in that it is both predictable and not. Most every one of them you'll see has Dragon Dance now, but what it chooses to butcher its opponents with is not as clear beyond the staple Earthquake. I would recommend taking one of Superpower or Stone Edge to fend off Ice types. Superpower has more power overall, more reliable accuracy, the ability to delete Hydreigon, Tyranitar and Bisharp (if Earthquake isn't enough), and finally an unfortunate drop that you can handle thanks to Dragon Dance. However, it's not quite as well-covering as Stone Edge would be, which takes care of Flying-types and Rotom-Heat, which Flygon would struggle to deal with otherwise.
The final move is up to you. Fire Punch would remove Ferrothorn and Scizor, First Impression can let you sneak a hit in if necessary, Dragon Rush is a strong move with poor accuracy but would help in defeating a Dracovish. If you want to run Dragon Rush on this set, that would be the time to use a Blunder Policy, as Dragon moves usually get poor coverage, defeating the purpose of the belt. Stone Edge also would benefit from the use of this item.
In all, Flygon's a wildcard that you could throw in to take care of specific threats your team struggles with. If you're using it in a tier above what it's designed for (OU as a UU mon), it struggles with Mamoswine with a 4x weakness to Ice Shard (yikes). Unaware Clefable will also not only wall Flygon but probably kill it before it can do sufficient damage.