This script I have here also makes it so players can't cheat and adjust ambience my pressing < or >.
Add this script to your scriptbank, call it whatever you want.
;Artificial Intelligence Script
;Header
desc = Make Ambience 0, Anti-Ambience-Cheat
;Triggers
:always:ambience=0,ambiencered=255,ambiencegreen=255,ambienceblue=255
:state=0:state=1
;End of Script
Add it to a trigger zone, and play your game!
Note: You can place your trigger zone anywhere. It's not actually 'triggering' anything by player touch, it just loads a script for you.
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About the fog, I suggest adding a flashlight, which is added in v120, which makes everything pretty creepy, then set the flashlight range low. So it's really freggin creepy.
Meh