Minecraft wiki entry for Defeating_the_wither, associated text: The Wither is built using 4 blocks of soul sand or soul soil and 3 Wither skulls. Soul sand and soul soil can be easily acquired in the Nether, specifically in soul sand valleys. In order to spawn the wither, build a T-shape using your four blocks of soul sand, and place a wither skull on top of each soul sand. This configuration is pictured to the left.