Minecraft wiki entry for Defeating_the_wither, associated text: You need to find a cave, preferably with a dead end, spawn lots of iron golems, then spawn the Wither inside of the iron golems. After that you need to run away as to not get killed by the explosions and wait, this method is pretty much risk free, but requires lots of iron. The Wither is killed in about 15 seconds using this method.