What item should I use on this Aegislash?
Ability: Stance Chance
Evs: 252Atk 252Spe 4HP
King's Shield (required)
Iron Head (STAB)
Shadow Claw (STAB)
Sacred Sword (Covers anything IH+SC can't hit)
Also should I use Shadow Claw or Shadow Sneak? I can't use a Spell Tag as I stupidly sold it to a PokeMart! Is there a way I can get it back?
Give Aegislash a leftovers so it can heal over time. It restores 1/8 of your HP every time you use king's shield. Also, you should probably replace its other three moves with shadow sneak, shadow ball, and toxic. Aegislash won't outspeed much even if you give it speed EVs, so it's better with a spread like 252 HP/252 SpA/4 SpD quiet.
Item for Aegislash
Personally, I think that the best item for Aegislash to hold is the Lagging Tail. This item makes Aegislash always move last unless it is using a priority move (which King’s Shield counts as). Spamming King’s Shield while attacking the next turn is really helpful since they attack you when you are in defense position, but then you can hit like a truck in offensive position, only to switch to defensive position in the next turn with King’s Shield.