you could use a script to disable fog and enable it,
set as 2 triggers one for turning on and of course the other for off,
i cant remember where i seen the script tho, i think it may have been a custom one made
and i think somthing like this infulance you into making one, oh have not even tried to work it all out as im no scripter.
:plrinzone:fog=1,fogred=255,foggreen=255,fogblue=30
Or another option is to use a decal like the puff puff or the blue decal and setup as fog/mist for the level required, and so you can manage it more effectivly, by size and where to position,
you don't just have to use one, you can have as many as you like, to cover what parts you need.
I'am not GOD but i can make you see again by taking my fingers out of your eyes and i can make you walk again by taking your beer away, but if you take my beer you will not walk again
