Cloudkill

This spell creates a 20'x20'x20' cloud of poison gas which moves at a rate of 10' per round under the control of the caster (so long as he or she concentrates on it). The gas kills outright any creatures of 3 or fewer hit dice or levels it comes in contact with; creatures having 4 or more hit dice or levels must save vs. Poison or die. The cloud persists for the entire duration even if the caster ceases to concentrate upon it.