Minecraft wiki entry for Enderman_farming, associated text: The farm is built in the End at least 128 blocks away from any spawnable block, so the endermen can spawn there only. A platform is built for the endermen to fall onto from spawning pads built at least 43 blocks above the platform, with rings built upward to prevent endermen falling onto an area that isn't the platform. On the 43rd block up vines are placed to break the fall, so the endermen take 19.5 hearts damage, leaving them on half a heart.