Minecraft wiki entry for Nether_survival, associated text: At the start of the fight, fire fully charged arrows at it. Watch out for the skulls and hide to restore hunger/health. If the wither breaks the obsidian, reinforce it. At half health, use your sword to hit the wither until it is dead. Do critical hits to kill faster. Once the wither is dead, pick up the nether star, and prepare the beacon base. (You cannot make the beacon yet because there is no way to obtain glass). Once you have all the mineral blocks you need, build the portal to the overworld. Set up your beacon to show you beat the Nether survival challenge. You can continue on this world and do what you want.