Dusk beast

A dusk beast was one of the ephemeras, a class of outsider native to the Plane of Shadow.

Description
A dusk beast appeared, in silhouette, as a two-headed lizard about the size of a man. However, being wholly composed of shadowstuff, it only appeared as a transparent shadow, making them excellent at hiding. Its four legs were hazy and faded from view before reaching its feet. However, its fanged heads and wickedly barbed tail remained in sharp resolution.

Combat
When confronted by an intruder, a dusk beast hid itself in the darkest shadow, then ambushed as many opponents as it could reach. Proving two heads were better than one, it could bite with both sets of fangs and also lash with its barbed tail. Thanks to its shadowstuff nature, it could extend its necks or tail to unnatural length versus its size, attacking up to 10 feet (3 meters) away, which could take targets by surprise.

Ecology
Dusk beasts were nourished by areas of shadow, but not darkness—they would starve in a place of utter darkness as much as they would in full brightness. They dwelled in environments that would provide deep shadow, like canyons, forests, and dim subterranean areas; these were guarded prime feeding grounds.

Behavior
Dusk beasts hated strong light and full darkness in equal measure. They savagely guarded their feeding grounds and sought to protect them, especially attacking those who brought light sources such as lanterns that caused their shadow-food to flee.

They lived in packs of up to five.