What's that thing that crawled out of the fog? RPG

A few days ago, a thick fog descended on your proud home. You didn't pay any attention at the time—fog and fog, so what?—but when the first screams rang out in the street, everyone realized the fog had brought something else with it... Death... That's when it all began: people abandoned their homes, fled, thinking they could escape it. Military alerts blared over the rooftops for days, mass evacuations ensued. But no one could explain what was happening. Then the phone line went out, then the water and electricity, and the fog continued to appear every evening...
The water supply is running low, the food in the refrigerator has gone bad without power, and all that's left is canned goods and a bag of chips. Something needs to be done.