What we've got here, is a... Well i'm not to sure at the moment to tell the truth. As I currently see it, this is a spirit of the Earth awakened by the war that rages, etc, etc. Timeless, eternal, this thing has been around since the dawn of time.
But what is it? The spirit takes the form of a large (make that mountainous), root like plant. A plant that uses the rubble, dirt, other vegetation, rocks and boulders to form a hardened defensive shell. Sort of like a hermit crab I suppose, except it's building from scratch rather than simply moving in...
Below is the first concept doodle. There are quite a few details to flesh out still, like what's going on with the right arm. I envisage it as more plant than rock, possibly some sort of weapon. I'll have to put pen to paper and find out.