Use the Double Clawshot to hook onto his tail when it isn’t attacking you. Then immediately use the Iron Boots to bring him down so its armor breaks. Do this a few times until he rips off his armor and it begins to rain and floating plants circle the battleground. Use the Clawshots on the plants and move around the dragon while dodging his flame attacks. When you get behind him use the Clawshot on his back and attack the jewel with your sword. Repeat this a few times to defeat him.