I've a got a map that is a bunch of floating pillars in the clouds. I thought that this fog would create the cloud, but after going on the valve devwiki, it turns out that env_fog_controller entity surrounds the player in fog, which would work fine for a zombie level, but it isn't what I want.
What I need is a cloud beneath the pillars, so once the player falls of the edge, he will fall through the clouds and a hurt trigger.