The Stalnox found on Satori Mountain
Hyrule Compendium Entry
A Stalnox is a monstrous boss that can only be found during the night, between 9:00 PM and 5:00 AM. It will not become active if Link is too close, or is watching it, however. If encountered during the day, it will simply be a pile of bones and will not come to life to attack Link. If Link engages a Stalnox in battle and morning arrives, the Stalnox will dig underground, fleeing the fight until the next night, at which point it can be battled again. Like its living counterpart, the Stalnox pursues Link, attempting to pound him to the ground or catch him between its hands. It is also able to pick up trees to use as weapons. Uniquely to the Stalnox, it can remove its ribs, collarbone, and even an arm to throw at Link. It is also able to dig up Bomb Barrels to hurl, which explode on contact. Shooting an Arrow into its eye will stun the boss as he hold it in pain, giving Link the chance to attack. However, when its health is past half, shooting the eye ball will detach it from its socket which will cause the Stalnox's body to drop into a pile of bones for a few moments. During this time, Link can attack the eyeball or even pick it up and throw it further away from the body, eventually, however, it will return to the Stalnox. Shooting the eyeball with a Bomb Arrow will automatically remove the eye no matter how much health the boss has. Once the eye has lost all of its health, or if the Stalnox and the eye are not reunited before the morning comes at 5:00am, the Stalnox is automatically defeated. Once dead, the Stalnox will drop Hinox Teeth and rare weapons.
The Stalnox fought within Hyrule Castle will reward Link with the Hylian Shield once it has been killed. Apparently, defeating it was once a test for Royal Guards to become knights. Link can only receive the Hylian Shield a single time by defeating this Stalnox and must purchase another from Granté in Tarrey Town if it is broken or lost.