Halloween // I need advice/ideas!!

HI! it's my 21st birthday this halloweekend! I wanna throw a costume party but I also wanna look like it's my birthday and so I have two really cute black dresses, one is like embroidered with sequins and the other is like a satin dress, could you pleaaase give me ideas on what I could dress up as using those dresses, or if you have any other ideas that would be great too!!