Known Region
The general area that the Palehorn Wightstag lives in is centered somewhere around the Black Fir Forest. Wightstags are spectral deer that inhabit the forest and are very rare and hard to track. Tracking them is not the issue here, finding their herd and then locating sheds is the harder part of this. The marrow is only able to be harvested from the antler sheds that fall off of the Wightstag around Spring.
Actually, I've recently heard rumors that the local hunter Niala has captured one. I should ask them about it.
Properties
Due to the natural properties of Ethereal and Death magicks, the marrow has a considerable amount of power to influence souls of people. It also has a known property of being able to retain memories quite well when added to a memory potion.
Unsure if the ingredient does this because it influences souls or if its because it is tied to the Ethereal magic.
..As An Alchemy Ingredient
Use case of this ingredient often include potions like Potion of the Hollow Path and the Vial of Shattered Time. It generally allows for communication with ones soul.
The vial of shattered time and the potion of the hollow path? Consider me intrigued...