Minecraft wiki entry for Best_biomes_for_homes, associated text: Soul sand valleys are by far the most trying biome to live in amongst the Nether biomes. The biome is coated in a floor of soul sand, making traversing slow. Skeletons and ghasts spawn frequently here, which when combined with the slowing nature of soul sand, can be very dangerous to the player. Soul fire is present in this biome, and occurs whenever soul sand or soil is set on fire. It deals double the damage of normal fire, but using soul sand/soil in certain crafting recipes can allow the player to craft soul fire variants of useful blocks, such as soul torches and soul campfires.