Minecraft wiki entry for Defeating_an_End_city, associated text: Shulkers may appear in inconvenient places, such as rooftops, outside walls, and even the undersides of platforms. To get to these shulkers, pillar jump to the shulker, or descend using sand. Try to shoot the shulker only if it opens otherwise the arrow will not deal any damage. If you get hit, place blocks and as you go up, and make sure you are directly over your pillar. You can also break the shulker's support block, thus forcing it to teleport, hopefully to a better location.