You see poison gas.
Location
Can be found anywhere outside of Protection Zones, but more common in swampy areas.
Notes
By stepping on one of these you will get the Poisoned status and take 5 points of damage on contact. Then you will lose damage over time, starting at 5 damage per turn for a total of 4x5+5x4+7x3+10x2+19x1=100 total damage. Its effects can be cured by the Antidote spell or Antidote Runes and the gas can be removed by using a Destroy Field Rune on it.
Looks the same as Plant Poison.
See also: Slime (Liquid), Earth Damage, and Poisoned
Dropped By
No creatures drop poison gass.