Just added all the viable sets of Aegislash in the OP, so focus discussion mostly on those sets.
Aegislash @ / Life Orb
Ability: Stance Change
Modest Nature
- Shadow Ball
- Flash Cannon
- Metal Sound/King's Shield
- Autotomize/ HP fire/ HP Fighting
A full special offensive Aegislash, this takes advantages of aegislash's great special attack and bulk.
You don't need Metal Sound and Flash Cannon. Iron Head hits the common Fairy-types harder (Florges, Sylveon, and Togekiss) and Tyranitar too, while you should use Hidden Power Ice in the third slot to deal with Ground-types.
How is a mixed set gonna sweep when it is too slow and has no kings shield to put it back in defensive form
The mixed set's goal is not to sweep but to wallbreak.
Seeing as there is a lot of confusion as to what the role of each set is, i am going to explain them:
King's Shield +3 attacks: The epitome of a tank. Can take a lot of punishment and check dangerous Pokemon such as Mega Lucario, Togekiss, Azumarill, and more, while hitting hard and being very difficult to hard counter.
Autotomize: Late-game cleaner. Aims to set-up and sweep during the final stages of the game, where its checks and counters have been weakened or eliminated. Shouldn't usually set up if Pokemon that can take a hit and OHKO back are still alive, or Pokemon that can outspeed and OHKO it even after an Autotomize are alive.
Double Dance: Boosting tank. This is one of Aegislash's most versatile sets as it can easily adapt to most situations. It can set up with Swords Dance against defensive teams or Autotomize against offensive teams and start dishing damage, while still being a great pivot and check to many offensive Pokemon.
Mixed: The definition of a wallbreaker, and an excellent one at that. Nothing in OU can avoid the 2HKO from it except from SpD Hippowdon (which gets 2HKOed if Shadow Ball drops its SpD on the first hit, which is bound to happen sooner or later) and physically defensive Mandibuzz.
Swords Dance: Depending on the item of choice, Leftovers or Life Orb, it either plays as a mix of tank and late-game cleaner (with Leftovers and King's Shield) or as a softener and late-game cleaner (with Life Orb and Shadow Claw).
Also, since i didn't see it mentioned anywhere, here is the best counter to any Aegislash set:
Mandibuzz @ Leftovers
Ability: Overcoat
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Foul Play
- Roost
- Defog / Toxic
- Taunt
Avoids the 2HKO from any existing set of Aegislash and 2HKOes any variant with Foul Play, or OHKOes if Aegislash used Swords Dance as Mandibuzz came in. It doesn't care about King's Shield because Foul Play's damage is based on the opponent's Attack. This set is also a phenomenal anti-hazard supporter, switching easily into most hazard users, getting rid of their hazards, and preventing them from setting up any more with Taunt, so that you can bring something in that can take advantage of them if they don't care about Foul Play. Toxic is for teams that don't need Defog and when combined with Taunt can make short work of many defensive Pokemon that are not immune to it. Shame that Foul Play is not available yet on the existing X and Y OU metagame.