Foaming Powder

When you add this 1-pound bag of green powder to a gallon of water, the two combine to form 50 cubic feet of thick green foam. Unless contained, in 1 round the foam fills a 5-foot-square to a depth of 2 feet. When multiple pounds of powder are used, the foam expands at a rate of one 5-foot square per round. Ground covered with the foam is treated as difficult terrain, but is otherwise harmless. After 1 hour, the foam hardens to form a buoyant material roughly the density of honeycomb. The cured foam is easy to cut, with hardness 0 and 5 hit points per foot of thickness. The cured foam breaks down over a few days, and even faster if exposed to water. Casting transmute mud to rock on uncured foam converts it into a soft, pumice-like stone (hardness 2, 5 hit points per inch of thickness).