They have red bodies and white masks and are found in Angler's Tunnel, Catfish's Maw, and Eagle's Tower. They can be defeated by delivering a sword slash to their backside, but even easier than that, their masks removed through the use of the Hookshot. Once their mask is removed, they can be dispatched with a simple sword slash. The Iron Masks' only attack is to come in contact with Link, which will do a half a heart of damage.
Oracle of Seasons
Virtually identical to their Link's Awakening counterpart, Link can defeat the Iron Mask in the same fashion. The Magnetic Gloves can be used to pull off the mask, which makes the enemy more easy to defeat.
Oracle of Ages
Much like in Link's Awakening and Oracle of Seasons, Link can slash at the Iron Masks' backside to defeat it. In Oracle of Ages, the Switch Hook or the upgraded Long Hook can be used to pull off the enemies' mask.