2018 art, featuring one of my more odd concepts...

This one originated as part of the Geoterra Project, which back in the day utilized a sort of "magic evolution" dynamic like certain popular fighting monster franchises. However, this one didn't have a set "stage", and any creature had a chance to become one of these shadow beasts provided they were evil or vengeful enough upon death, or their fate was particularly traumatic. Or something to that effect.
They tend to not have a whole lot of memory of their past lives and can act rather aggressively depending on the circumstances. Typically "bound" to their place of death, their grave site, or some personal item they valued greatly, and are very defensive of that site or item.
Immune to most physical attacks, follows typical "undead monster" rules in regards to being harmed by healing magic.