I think this would be completely awesome if it were slightly tweaked. The fog/mist should be filled with zombies and it also carries the air borne infection. The rag and gas mask help prevent the infection as a % over time. Meaning that the rag would prevent the infection 25% of the time every 5 mins. and the mask should be 95% of the time every 5 mins (because hell maybe a zombie pulled it down or off for a split second). The mist should be more like fog with yellow-ish snow flakes in it while regular fog still patrols the game. The fog should only appear during adverse weather or from dusk to dawn. The game needs weather systems to be implemented in a sense of clouds being projected on the landscape so when a big cloud comes so does the mist. This way its not mid-day and fog rolls in, it also makes sense that the fog travells in cold/warm fronts as so do clouds and weather systems. The clouds idea is just my 2cents that would also make the game looks visually better :P so I suppose it doesn't need to be implemented.