Ok! Got some work done on this tonight. I think it's starting to come together! I solved the "mud" issue by using baby powder and mixing it with paint to create almost a brownie mix. I then rubbed this into the areas I wanted it to stick too. Finally, I covered it with Dullcote to seal it.
I want to add some tonal range to the mud and then "scape" some off like the reference AMP to complete it. I believe I'll also have to get one of the Avatar action figures to complete it. The box says "most 3 3/4" figures.. However, I believe they meant tiny figures only with no armor, or helmets. =)
Here are todays pics. The flash tends to make the entire piece look washed out. I can assure you that in nature light the mud looks like mud caked onto dark grey.