Here are costumes that deal with ghosts, such as well, ghosts, paranormal investigators, ghost hunters, psychics, fortune tellers
Notes on ghost-themed roles by Dr. Bon:
Ghosts costumes can nearly be anything if you stick on a gray wig and make your face gray with makeup. And a bit of a hollowed eye tops it off by putting a dark shadow underneath each eye. But you can be a traditional cute ghost like Caspar or opt for a mean, scary ghost. Or, maybe you can be any occupation you wish but put a ghost twist on it, such as a Victorian lady ghost, a train conductor ghost, a prom queen ghost, etc.
Paranormal investigators usually opt for a more Gothic-inspired look than cheery, trendy Cher from Clueless attire. Think Elvira meets Lora Croft, and you are there. Grab old electronics and call them whatever you wish, such as a ghost fart detector (yes, I'm childish, but if you did that, you'd get some laughs), or grab an old remote and call it an EMF meter. I mean, how many people would know what one looks like?
Ghost hunter: you can opt for the Ghostbuster costume or spice it up and make a unique version. Save the next cardboard box you get shipped to your house, tape it shut, and paint it silver or black. Glue a ton of items on it that look like controls and then affix straps to it so you can carry it like a backpack.
Fortune Teller/Psychic: this might be a bit cliche as those in these occupations nowadays simply can look like everyone else, but if you want to stick to the cliche costumes - opt for flowing poet shirts, long skirts, tons of jewelry with crystals of all kinds (as they are for protection and other things), bangle bracelets, rings with crystals, and a golden head chains. Do not forget your magic eight ball or fortune-telling crystal ball, or some tarot cards. I've been told you shouldn't mess with ouija boards, so don't bring one of those :)