Minecraft wiki entry for Skyblock, associated text: Hostile mob farms are very important because they are a source of bones, strings, redstone dust, iron ingots, potatoes and carrots, among many other drops. Building a mob farm is mandatory to get the crops to start crop farming. It is also an abundant source of rotten flesh, which you can now eat instead of apples. Multiple mob farms designs are explained in the page Tutorials/Mob farm, however, the vast majority of efficient designs need water or redstone circuits.