I've been using this set for Doublade and it works pretty well!:
Doublade @Eviolite
Trait: No Guard
EVs: 252 HP / 252 Atk / 4 Def
Adamant Nature (+Atk, -SAtk)
- Swords Dance
- Substitute
- Shadow Sneak
- Sacred Sword
This is the only set that's not outclassed by Aegislash imo. Try to get a free Sub on things like Ferrothorn, Defog Mega Scizor which has been gaining usage lately, physical Mega Lucario, Talonflame locked into Brave Bird etc. Then use Swords Dance to get a respectable 700 Atk, and attempt to sweep with flawless coverage including a priority move and a move that ignores defense boosts (hey, it has helped me out before against Baton Pass :P).
People often don't expect Substitute (in fact sometimes they have never seen a Doublade before at all) so they'll switch in stuff like Greninja expecting SD, resulting in them taking a lot of damage. This set works the best with Dual Screens. Klefki is by far the best partner: Priority thanks to Prankster guarantees your screens, and you can even paralyze some pokes or setup some Spikes while you're at it, both of which Doublade appreciates a lot. In fact, look at some calcs that show Doublades bulk behind screens:
4 SpA Rotom-W Hydro Pump vs. 252 HP / 0 SpD Eviolite Doublade through Light Screen: 72-86 (22.3 - 26.7%)
0 Atk Landorus-T Earthquake vs. 252 HP / 4 Def Eviolite Doublade through Reflect: 70-84 (21.7 - 26%) -- 3.6% chance to 4HKO
I found these two switchins, bulky Landorus-T and defensive Rotom-W to be very common. Both fail to break Doublades Sub most of the time. This means that with some lucky damage rolls (the odds are in your favor) you can setup to +6 by alternating between Sub and SD, then finishing them off with Shadow Sneak. The fact that this is possible to begin with shows that Doublade definitely has some viability in OU. I mean, with Reflect you have an effective 1010 Defense without a +Def nature or Def EV's and Landorus-Therian's uninvested Earthquake doesn't even break your Sub reliably. That's pretty bulky for a pokemon that has 350 Atk to utilize (Talonflame dies to +2 Shadow Sneak after SR for example, while Doublade tanks a CB Flare Blitz).
It definitely needs support to be effective, but can perform very well with it.