Hologram

Well my friend, shorty-productions, and I are working on a brickfilm, Agent C-O-P . It really has been an on off project, so I decided to start making my own film about the Halo:The Fall of Reach book. It has an AI, artificial intellegience, which is sort of like a hologramic person. I was wondering how I should make a minifig look sorta ghostly or see-through. Please help. Thanks in advance!