The Sun Skeleton Test Link [exclusive]: Beasts In

At dusk the beasts returned to the dust, bones glinting like promises that refuse to die. The sun folded itself beneath the horizon with a small, satisfied sigh. In the town, the living kept what the beasts had returned and mended what could be mended. They learned to wait for the light, to let their secrets find steady ground, and to take whatever polished fragment the world would hand back—because some truths, exposed to the sun, can be unbearable until they become instruments you can play.

An oppressive, vital environmental force, likely acting as a survival mechanic (resource management, time-of-day mechanics). The "Skeleton Test Link": Decoding the Mystery beasts in the sun skeleton test link

If you have more information about where you saw this, like: (monsters, animals, creatures) At dusk the beasts returned to the dust,