This spell generates a bank of fog, similar to a fog cloud except that its vapors are ghastly yellowish green and poisonous. These vapors kill any living creature with 3 or fewer HD (no save) and cause creatures with 4 to 6 HD to make Fortitude saving throws or die. Living creatures above 6 HD, and creatures of 4 to 6 HD who make their saving throws, take one step of Constitution damage on your turn each round while in the cloud. Additionally, all living creatures, regardless of HD or whether they make their saving throw, take poison damage (equal to the spell’s save DC − 10, divided by 2) on your turn each round while in the cloud. Holding one’s breath doesn’t help, but creatures immune to poison are unaffected by the spell.

Unlike a fog cloud, the cloudkill moves away from you at 10 feet per round, rolling along the surface of the ground. (Figure out the cloud’s new spread each round based on its new point of origin, which is 10 feet farther away from the point of origin where you cast the spell.)

Because the vapors are heavier than air, they sink to the lowest level of the land, even pouring down den or sinkhole openings. The cloudkill cannot penetrate liquids, nor can it be cast underwater.