Knucklemaster

Knucklemaster is a boss in, who resides in the Skull Woods, guarding Sage Seres's painting. It appears as an organic hand encased in a metal gauntlet, with an eye in its palm.

Location and Access
The Knucklemaster's lair is located off the middle of a dark corridor at the bottom floor of the Skull Woods. It is fought in a room with many cracks on the floor. Beating it opens up a stairway leading outside, where Seres' painting is held.

Appearances and Weaknesses
Knucklemaster appears as the boss of the Skull Woods. Its main attack involves clutching into a fist and ramming Link. This attack can only be avoided by jumping out of the way with the Tornado Rod, or turning into a painting. This causes Knucklemaster to crash into the wall and get stunned, exposing its vulnerable eye. After recovering, it will attempt to squash Link repeatedly. This is not only dangerous on its own, but it also destroys the fragile parts of the arena, making it harder to maneuver. After sustaining enough damage, Knucklemaster will get faster and attempt to squash Link more often, but the strategy to defeat it remains the same. Upon the monster's defeat, a passageway will be revealed, leading to Seres's painting.

Glitch
It is actually possible to skip the fight against Knucklemaster via a glitch, as seen here. If Link stands near the upper wall of the arena and uses the Tornado Rod at the same time Knucklemaster attempts to ram into him, it is possible to leave the arena and reach Seres's painting without fighting the boss. However, doing so will result in the Heart Container Knucklemaster yields to be unobtainable.

Trivia

 * Knucklemaster is a portmanteau of knuckle, a part of the hand, and master, a suffix used in many hand enemies.