King Dodongo is the boss of the Dodongo's Cavern. you beat him by running around and throwing a bomb in his mouth when he breaths in to burn you with fire then hit him as fast as you can while he is stunned. You do this three times but after every time he rolls around and trying to kill you so just go in a corner or run away near the fire pit. After the third time he will go int the pit of lava and die. You will get the Goron Ruby and a heart piece.