The stone and bones look fine and clean. More stages, could be good, for more contrast.
The part that leaps out as could do with a bit more is the material. I don't know the context of the mini, is it leather or skin yanked off a victim or two? As it is, just brown, it's not suggestive of being anything and could do with some shading and highlighting to address that, the contrast would make it *pop* more.
Could maybe add some some brown staining on the stone, if the bones have been there for some time the bone marrow could leak juicyness. Could do similar with the nails pinning the material to the stone, have them rusted with a couple of millimetres of rust staining running down.
Overall, good and clean and paintjob, could benefit from a few more stages in shading/highlighting for contrast.