[Scenario]

Hey guys. I am currently writing up some plans for a new server I'd like to begin working on, one of the key factors of the server will be NPC's driving/walking around. I doubt it's possible, but is there a way to make NPC's kind of "ghostly?" As in, you can walk through them without problems.

Again, even though I doubt it's possible, if it is, could someone give me a brief explanation on how to do such a thing?