Minecraft wiki entry for Wither, associated text: Upon noticing a player or mob, the wither flies to a random location and hovers in place. It shoots 3 black wither skulls and one blue wither skull before flying to another location. The time between each shot decreases as the wither loses health. On Normal difficulty or higher, if the wither has targeted an entity but cannot find a location to path find to, it shoots random blue skulls in a random direction along with the skulls directed toward the target.