Knucklemaster is the boss of the Skull Woods, a giant disembodied hand that emerges from the ground. The battle takes place in a circular arena. In its first phase, Knucklemaster will try to smash Link with its fist. Dodge its attacks and wait for it to slam its hand onto the ground. When it does, its palm will be exposed. Quickly hit the glowing eye in its palm with your sword.
After taking damage, Knucklemaster will retreat into the ground and then emerge from a different spot. It will also start to summon smaller hands that will try to grab Link. Defeat these smaller hands quickly. When Knucklemaster slams its hand down again, repeat the process of hitting the eye in its palm. Be careful of its sweeping attacks and the smaller hands. After enough hits, Knucklemaster will be defeated, rescuing Impa and obtaining another Lorule Sage.