Immortal Seductress from buycostumes.com.
Available in sizes 16-18 & 18-20, listed at $36.99
Pros: cute fishtail silhouette with split front and draped "cape".
Cons: burgundy, not purple. no awesome collar.
Maleficent costume hat at both amazon and buycostumes; $12.99-24.99
I like that it has burgundy stripes, which will tie in with the dress.
No one will mistake that silhouette for anyone other than our beloved sorceress.
Maleficent staff featuring Diablo; $19.99.
I think I want to get this just to have around the house. It's so damn cute!
And if total cosplay is more sexy to you, here's the full gown that looks like it leaped right off an animation cell.
Available in sizes 1X and 3X at buycostumes.com; $74.99