Dodongo is the boss of Dungeon 2. This rhinoceros-like creature is immune to your sword attacks. To defeat Dodongo, you must use your Bombs. Dodongo will patrol the room. When it opens its mouth, quickly place a Bomb directly in front of it. If timed correctly, Dodongo will swallow the Bomb, causing it to explode internally and stun it. While stunned, Dodongo will be vulnerable to your sword attacks.
You'll need to repeat this process several times. Each time Dodongo swallows a Bomb, it will take significant damage. After being stunned, Dodongo will recover and resume its patrol. Be careful not to get too close when it's not stunned, as it can charge at Link. Ensure you have a good supply of Bombs before entering this boss fight. If you run out, you'll need to exit the dungeon and purchase more. Upon defeat, collect the Heart Container and the second piece of the Triforce of Wisdom.