Using Substance Painter I could easily gauge the look of the mossy areas, before scattering Megascans moss on top with XGen.
Base Mesh with Displacement & Normal Maps.
Sculpt vs base mesh.
Damage pass in Zbrush - mostly alphas, trimed edges and a bit of NoiseMaker.
Base Mesh
Rather than trying to model the legs in maya, I just used booleans in Zbrush with simple shapes and zremeshed the result.
Blockout