Darkhammer

The Darkhammer (ハンマーナック, Hanmaanakku) is the Mini-Boss of the Snowpeak Ruins in Twilight Princess. When defeated, the creature drops the Ball and Chain (not in a treasure chest), an item usable by Link. Following that, Link may proceed to open a chest Yeta thought contained the Big Key, but really had Ordon Goat Cheese.

Perhaps this is in reference to A Link to the Past, in which Princess Zelda, imprisoned in a cell in the dungeon of Hyrule Castle, is guarded by a knight wielding a ball and chain. Upon defeating the knight, Link receives the Big Key.

Darkhammer is possibly a type of Lizalfos.

Strategy
Darkhammer will continuously guard his body with his massive Ball and Chain. In order to defeat him, Link must use one of four strategies. The first is to Clawshot a target behind him as soon as he motions to throw his weapon. He will then pause to pull in his weapon, giving Link the opportunity to slash at his exposed tail. The second is a quicker, but much riskier way. Wait until a split second before his weapon lands, and then roll behind him, swinging Link's sword at his tail. The third technique is to instantly kill him by using Mortal Draw on his tail. However, the timing required makes it tricky to perform. A fourth is to simply run behind while he swings his weapon over his head, and slash his tail repeatedly. The blows will stun him and keep him from attacking.

Trivia

 * The Darkhammer resembles the Darknut miniboss within the Temple of Time, not only by its prefix 'Dark-', but also because of its heavy armor suit and large weapon of choice.
 * The Darkhammer resembles the Ball & Chain Trooper, which is a recurring enemy in The Legend of Zelda series.