The Miasma is a thick, grayish, slow-moving fog. Generally heavier than air, it seems to mostly settle in lower elevations — but not always, as at times it covers hills and valleys with equal depth. The edge of large areas of miasma is a wall that can rise as high as 50 feet or more, while small pockets (covering as little as a square mile) rise only about 20 feet or so.
Normally the miasma moves overall only a few inches every year, there are however times when it can dramatically shift. It has been known to sometimes engulf an area of several miles or retreat a like distance in a matter of a day. It also fluctuates, generally receding during full moons and expanding on the new moon.
Any living creature caught in the miasma can expect to wither and die in a matter of minutes. The mists effect body and mind, making a person disoriented and confused as well as weaker. Those the succumb to the deadly mists arise soon after as the mindless undead; forever hungering for the flesh of the living.