Aquamentus is the boss of Dungeon 1. This green, one-horned dragon will be your first major boss encounter. Aquamentus moves slowly from side to side and spits fireballs in groups of three. The key to defeating Aquamentus is to stay mobile and attack its head. Your Wooden Sword is your primary weapon here.
Position yourself diagonally from Aquamentus to avoid its fireballs, then move in quickly to strike its head with your sword. After landing a few hits, retreat to avoid its next volley of fire. Repeat this pattern: dodge, attack, retreat. If you have the Blue Candle, you can try using it, but your sword is generally more effective. Aquamentus has a relatively low health pool, so with consistent attacks, it will fall quickly. Upon defeat, collect the Heart Container to increase your maximum health, and then claim the first piece of the Triforce of Wisdom.