Minecraft wiki entry for Ultra_hardcore_survival, associated text: If you have played Hardcore mode many times and are comfortable with it, and want an even bigger challenge, try Ultra Hardcore Mode. Ultra Hardcore mode is like Hardcore, but to add to the challenges of hardcore, you don't naturally regenerate health. This difficulty is extreme, so it is advised to try hardcore mode first to gain extensive experience, and move on to this difficulty when you think you are ready.