Unique? Try Anime cosplay! For instance, I'm going as Crona from Soul Eater, that's pretty unique. The best part about Crona is that s/he's genderless and doesn't have many traits that distinguish it's gender, so anda can go as it no matter what gender anda are. An awesome touch is getting the sword atau the Ragnarok stuffed animal to put on your head to mimic how it get's tortured sejak Ragnarok all the time.
honestly, anda dont have to be from a movie. ask them to think of somthing horrifying, and dress like it. i make my own costumes, so its acually quite easy if anda know what to do/use. if anda choose this and need help, just write on my wall.