It's going to be pretty hard to map a whole ghost, unless it's just a pattern like checkers, etc. But if your going to map it like a whole person, like Skylarrr said, not sure how you'd be able to do that, or ghosts that are your textures you have on, just transparent, or they can be like "Ghost Texture Head", "Ghost Texture Hand", etc. And they'd be pretty cheap too, like 1k tc each or something (also people can do pure ghosts with textured ghosts :O)
~kinda supported