Stallord

Twilit Fossil Stallord (蘇生古代竜 ハーラ・ジガント) is a recurring enemy in the Legend of Zelda series. Stallord is the skeleton of an ancient, dead beast found inside the Arbiter's Grounds. This boss battle has been regarded by many as one of the greatest boss battles in the Legend of Zelda series. Its name comes from the "Stal-" prefix (Staltroop, Stalfos, etc) and "lord", and could thus be called a "Stalfos lord"---or, seeing as the "Stal-" prefix refers to skeletal enemies, a "Skeleton Lord".

Stallord has a roughly humanoid upper body standing up from a pit of sand, and a horned animal head comparable to a goat or dragon. Its lower body is never seen (in fact, whether its lower portions were even present at the time is unknown). The music played while fighting Stallord is a remix of the music that plays during boss battles against King Dodongo and Volvagia in The Legend of Zelda: Ocarina of Time.

The Legend of Zelda: Twilight Princess
Link comes upon Stallord while searching for the Mirror of Twilight in the Arbiter's Grounds. Zant then appears and plunges a magic sword into the beast's skull, bringing it back to life.

Battle
The only way to damage Stallord is by tackling its lower spinal vertebrae with the Spinner. Stallord will try to keep Link away by summoning Staltroops and spitting blasts of dark fire from its mouth. Knock away Stallord's three lowest vertebrae, and the beast will fall. The sandpit recedes, and the battle appears to have been won.

However, Stallord comes alive once more. Its head starts floating and pushes Link into a large circular pit. Use the Spinner to chase Stallord, which again spits fireballs at Link. He avoids these by jumping between the two walls. Jump into Stallord's head with the Spinner, and it will fall to the ground. Once in this vulnerable position, slash the blade embedded in its skull as many times as possible before it reawakens. Repeat this process and the Stallord will fall for the final time.

Video
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Link's Crossbow Training
Stallord appears as the final boss of the single-player mode in Link's Crossbow Training. This battle takes place in the desert beyond the Arbiter's Grounds (visible in the background) rather than within the Grounds themselves. To defeat Stallord in this timed battle, Link must destroy three red targets, one on each of Stallord's hands and on his head, while avoiding Stallord's fireball attacks and destroying the clouds of Bubbles the skeletal lord releases.

Speculation
Stallord may be the dragon Volvagia from Ocarina of Time, as he was never revived in the Twilight Princess timeline and has a very similar appearance (besides being only a skeleton), abilities (spitting fire) and the same music. But this is unlikely, as it is considerably bigger than Volvagia was, and it is found in Arbiter's Grounds which is directly across from Death Mountain where Volvagia had lived. There are also differences such as Stallord having some hair around its neck, while Volvagia had a mane of flames. Stallord's dental structure also differs from Volvagia's, Stallord has ten digits in all while Volvagia only has six. Stallord also has quite long arms, while Volvagia had very short ones.

There was also a belief that Stallord is King Dodongo, another boss from Ocarina of Time, which is somewhat similar in appearance to Stallord. This theory could be likely because of the fact that part of the music from the battle with King Dodongo is used in the battle against Stallord, when he dies he leaves behind remains that could be revived, and that King Dodongo was of a similar size. This is discredited based on several differences similar to Volvagia's (arm length, digit number, general proportion of limbs, torso, and head).

It is also possible that Stallord is based on General Onox's dragon form from Oracle of Seasons. The preportions of arm length, the wing span, and the facial structure are quite similar. The fact that Stallord also has no lower half is quite similar to how Onox has a tail and no hind legs.