The Master Stalfos is the main Mini-Boss of the fifth Dungeon in Link's Awakening, Catfish's Maw. He wields a skull shield protecting his left side, and a fairly large sword. He is a very unique mini-boss considering that Link must find and defeat him four times (in the correct order), a first for the Zelda series.
To attack, this enemy will try to jump and land on you, quickly dodge, and attack his unprotected right side. Once you strike him, he will crumble, and you must immediately place a bomb on him before he stands up again. Repeat this until he is defeated. After defeating him for the fourth time, you can claim the Hookshot.