Stalnox

Stalnox are a special type of Stalfos formed from the gigantic skeleton of a deceased Hinox. They debuted in The Legend of Zelda: Breath of the Wild where they serves as overworld Bosses. Like every other Stalfos, they are unable to stay formed under the light of the sun and will crumble into a pile of unanimate bones once the sun start to raise. One was actually fought by the Royal Guard as a test to become knights.

Battle
The Stalnox will only appear during 9:00 PM and 5:00 AM but its bones can be found lying on the ground during the day. Like regular Hinoxes, the Stalnox takes advantage of his enormous size and will attempt to either pound Link into the ground or crush him with its gigantic arms. Being a Stalfos allow the Stalnox to perform some attacks that the regular Hinox cannot like using one of his ribs, collarbone, and even an arm as a projectile that it can throw at Link. It can also dig up Bomb Barrels from the ground and throw them at Link. Since the Stalnox has no skin and its bone structure is too hard to be damaged by Link, the hero must shoot Arrows as the Stalnox's eye to make it fall out of its socket and inflict damage to it until it dies, which will reward Link with Hinox teeth and some rare weapons. The one in Hyrule Castle wiill also reward Link with the Hylian Shield.

Hyrule Compendium Entry
"The mere remains of what was once a giant monster known as a Hinox. These skeletal beasts appear at nighttime. Much like their living counterparts, the Stalnox will tear entire trees from the ground to use as weapons. Furthermore, even if it appears defeated at first, it will keep coming back for more as long as its eye is left intact."