Iron Knuckles are generally regarded as the deadliest regular enemies in Ocarina of Time. Each of their attacks costs a massive four hearts and on top of that, their attacks could only be dodged, not blocked. They serve as the minibosses of the Spirit Temple. At first, they appear to be statues holding gigantic axes, but once struck, they start to move and the battle begins. A Brainwashed Nabooru in Iron Knuckle armor also appears as the boss of that dungeon.
They later appear in Ganon's Tower, with two colors, one black, and one white. It is wise enough to only strike at least one.
In the game Majora's Mask, Iron Knuckles play the same role as Ocarina of Time. It is also notable that their armor appears in the curiosity shop.