Minecraft wiki entry for Advancement_guide, associated text: To get this advancement, you need to respawn the ender dragon. This is possible by placing end crystals on certain blocks of bedrock that surround the exit portal in the End. The exit portal is surrounded by three bedrock blocks on each side, with blocks connecting each of the sides, for a total of 16 blocks. Place an end crystal on the middle block of each of the sides. This will respawn the end crystals on the obsidian towers, as well as the ender dragon herself.