I'm curious if there's a shader in the Source engine that would allow for a ghost effect, where the entire model is rendered at a certain opacity level relative to everything else. Compared to what happens with, say, the holograms in Half-Life's hazard course, where you can see where polygons overlap on concave shapes. The ability to receive lighting from the map is optional, but appreciated. And yes, I checked the wiki. I didn't see anything of the sort, but I know it's not comprehensive.