Minecraft wiki entry for Defeating_the_ender_dragon, associated text: If you are not sure that you have destroyed all of the crystals, let the dragon fly away. If you see a healing beam, then there is still a crystal left. Once the last crystals have been destroyed you can start to attack the dragon. You can also swap out your extra blocks with your water bucket, because you do not need the blocks anymore. There are many ways to attack the dragon, but there are many things to watch out for.