Darkhammer

The Darkhammer 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 thinks contains the Big Key, but really has Ordon Goat Cheese.

This is likely to be a 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 has a somewhat reptilian appearance, particularly with his tail, and is possibly a relative of Lizalfos. Hyrule Historia concept art appears to back up this theory.

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. Link waits until a split second before his weapon lands, and then rolls 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.

Midna's hints

 * Doesn't he know how dangerous that is, swinging a big metal ball around in such a small place? It's too dangerous to get close to him, so let's use the ceiling to get over to his other side! -At the beginning of the battle
 * Hey, look at his backside... He's covered in strong armor all over, but his tail's exposed! After he throws that ball, do you think you could get behind him and whack his tail over and over? -After he throws the ball the first time
 * That's the way! Go for him after he throws that ball! -Remainder of battle

Trivia

 * The Darkhammer resembles the Darknut miniboss within the Temple of Time, not only by the "Dark" prefix, but also because of its heavy armor suit and large weapon of choice. It's Japanese name ends with, same as Darknuts and Iron Knuckles, also implying a relationship to both enemies.
 * The Darkhammer also resembles Doomknocker, a bulky armored knight from The Adventure of Link who fights with a flying spiked club.
 * As stated above, the Darkhammer resembles the Ball & Chain Trooper, which is a recurring enemy in The Legend of Zelda series.
 * Similar to the Iron Knuckle, the Darkhammer stands lifelessly when Link finds it. It then comes to life when Link attempts to exit the room.
 * The Darkhammer is the only Miniboss to be defeated in a single hit with the Mortal Draw. Ook, Dangoro, and the Deku Toad are all fought before the Mortal Draw can be learned, while the Death Sword, Temple of Time Darknut, Aeralfos, and Phantom Zant take strangely minor damage from the attack.