*** warning ***
I did this and it has cost me dearly...
My wife had suspicions that I would like to be either a cross dresser or transgender. I went to a Halloween parties in female mode. The next day I came out to her (I couldn't take it any more) and we went to another party which I re-wore the same costume.
That is one of the things she the kept "throwing back on me" as I started to transition. (In very negative terms)
So if your spouse is not okay with your choice of costume, don't do it!!!
*** End warning ***
There are two I might choose:
Evie
Evil Alex
I'll throw in Emma but she's never dressed in a sexy out fit.
If you go to
http://disney.wikia.com/wiki/CategoryWitchesYou'll get a list of all of them.
I would look for a whispy flowy black dress with a pointy hat, black fishnet stockings with 4 or 5 inch heals. No broomstick unless I thought I would need it to fight of the boys.

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