Don't use this:
Aegislash @ Leftovers
Ability: Stance Change
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Swords Dance
- Shadow Sneak
- Sacred Sword
- King's Shield
Why it's bad: This set gets walled to hell and back by pretty much any decent defensive Pokemon. It's also extremely prone to burns. Skarmory and Gliscor literally never give any fucks, pretty much regardless of boosts and the all-round versatility of this set is poor. Stance Change is both a blessing and a curse, and it forces lots and lots of mind games. However, in its frailest form, Aegislash won't be sticking around long and can often find itself cornered by a Super Effective non-contact move like Earthquake which will doubtless KO it after the user has tanked a Shadow Sneak.
Instead, use this:
Aegislash @
Weakness Policy
Ability: Stance Change
EVs: 252 HP (Or 252 Atk) / 252 SpA / 4 SpD
Quiet Nature
-
Shadow Ball
- Shadow Sneak
- Sacred Sword /
Flash Cannon
- King's Shield
Why it's better: This set alleviates those nasty situations where you can't deal enough damage to KO before taking an EQ in Blade Forme. Aegislash's monstrous defences allow it to tank many a super effective hit when in Shield Forme. Getting a
DOUBLE BOOST from Weakness Policy in this way is insane, as very few counters / checks are safe when Aegislash reaches +2 in both offences. Here are a couple of calcs...
+2 252 SpA Aegislash-Blade Shadow Ball vs. 252 HP / 0 SpD Skarmory: 390-459 (116.7 - 137.4%) --
guaranteed OHKO
0 Atk Gliscor Earthquake vs. 252 HP / 0 Def Aegislash-Blade: 356-422 (109.8 - 130.2%) --
guaranteed OHKO
4 Atk Hippowdon Earthquake vs. 252 HP / 0 Def Aegislash-Blade: 414-488 (127.7 - 150.6%) --
guaranteed OHKO
+2 252 SpA Aegislash-Blade Shadow Ball vs. 4 HP / 0 SpD Mega Garchomp: 304-358 (84.9 - 100%) --
6.3% chance to OHKO
Etc, etc --> Overall a much better set.
NOTE: Flash Cannon isn't recommended by me, although it can be used to get by certain threats much easier (such as Mandibuzz). Overall though, Sacred Sword is a far superior option in my opinion.
EDIT: Thanks to dbzmeriogeno for pointing out my idiocy in the EVs and natures previously!