So it's pretty easy to use the mask/normal-map/depth-estimation from Relight in Blender. Does a pretty good job even for fantasy art.

Now if only I had a nice spooky background to go with. 👻

Edit: Added one based on Moonlight Affair (AlexisAnt0nio - Creative Commons CC BY-SA 4.0).

Pomegranate lig by neltruin.