Minecraft wiki entry for Defeating_the_ender_dragon, associated text: To respawn the dragon, place four end crystals one on each side of the exit portal. The crystals that are placed instantly deactivate the portal, shoot beams at the tops of the towers, and reset the crystals and cages on the towers. Afterward, all of the crystals shoot beams into the sky in harmony. The player hears an extremely loud roar and see a massive explosion, which resurrects the dragon to begin the fight again.