I just noticed that my set doesn't have enough EVs, probably a typo. It should be 252 HP / 120 SDef / 136 Atk. I also noticed that Doublade can't learn King's Shield (which is weird, considering I was able to use it on PS, but it's probably updated now), so it should be running either Shadow Sneak or Rest. Additionally, there should be no reason why Doublade (or Aegislash for that matter) is running Night Slash, considering it serves no additonal coverage that Shadow Claw doesn't cover (also, it's resisted by Fairies). A good rule of thumb I use is to never run Dark attacks on Ghost types (unless it's Sucker Punch or Pursuit), and never run Ghost attacks on Dark types. Speaking of sets, I came up with another one.
Defensive Swords Dance
Doublade @ Eviolite
Ability: No Guard
EVs: 252 HP / 4 Def / 252 SDef
Careful/Impish Nature
- Rest
- Swords Dance
- Shadow Claw/Iron Head
- Sacred Sword/Sleep Talk
This is a potentially good defensive Swords Dance set, the only problem being the two turns of rest. I can't find the perfect place to put Sleep Talk, so it's stuck as just another set until then. Again, Gyro Ball can be used in place of Iron Head alongside a -Spe nature with 0 IVs.
After playing with Doublade more, it's actually a nice middle road between Aegislash's Shield and Blade form. Doublade is actually more physically defensive than Aegislash due to Eviolite, and it doesn't have to rely on Stance Change or King's Shield to take a hit. The only thing I find missing is leftovers recovery (which you can stall for on Aegislash) and slightly higher special bulk. If serebii's information on No Guard is right, then that means in a match of Doublade vs. Aegislash, Doublade can do massive damage vs. Aegislash if you predict playing against Shadow Sneak/Claw and King's Shield correctly.
I've compiled a list of pros and cons when deciding between Doublade and Aegislash.
Aegislash Pros:
- Leftovers recovery (stalling with King's Shield is a plus)
- General item use (life orb, choice band, etc.)
- Usable special bulk (can survive STAB'd SE attacks and KO back)
- Can run special attacks for surprise value.
Aegislash Cons:
- Unless you have good predicting skills, an experienced opponent can play around your Aegislash
- Pretty much needs King's Shield to be useful.
Doublade Pros:
- Fairly straightforward compared to Aegislash, much easier to use and avoids potentially risky mind games.
- Has an easier time setting up without having to use King's Shield to do so safely.
- Much bulkier than Aegislash physically, even without investing in Defense.
Doublade Cons:
- Needs Eviolite to maintain its niche.
- Considerably weaker than Aegislash unless you invest in attack.
- Needs investment in Special Defense, even with Eviolite.
- Ability hinders it more than helps it (unless in a case such as vs. Aegislash)
Although Doublade has potentially good Pros, there are far too many cons outweighing it. Aegislash is better for the specific role of either outright walling a threat or sweeping. While Doublade is a great middle road between those two roles, the choice between Aegislash vs. Doublade really depends on personal preference more than anything else.
OP should update with this info.