My advice:
Paint it to be what ever you want it to be... maybe add a little green stuff too... that way you can feel confident that it will become what you make it to be when painted.
I honestly can't tell what it actually is... some times I look and see an Ork skull laid on it's side and smashed into the mud... then I blink and other times I see a Ripper Nid being smashed into the mud... then I turn my head and it looks like a gray rock on top of armor and junk...
Good luck