So it wants both Shadow Ball and Sacred Sword?Without Shadow Ball, Aegislash loses a ton of its potential as it loses its most spammable STAB move, which compromises a its ability to break walls so well. It can (and often should) use Sacred Sword as well to hit its best check, Bisharp, on the switch, so you don't really miss out on anything by using Shadow Ball either.
Also, a few other things: Life Orb is a pretty bad item on Aegi since its fantastic natural bulk is a lot of what makes to so great. Also, your set has waaaay too many EVs. Finally, Aegislash is in no way checked by Chansey since Chansey cannot damage it back.
Is it better to dump King's Shield for an offensive set though and swap it in and out often?
I noticed the the 252 SpD should have been 4.
And I meant without Sacred Sword Aegislash can't do much to Chasney/Blissey and they're kind of at a stand-off doing nothing (without Toxic on Aegislash).