Thanks ajlafleche, I really appreciate your comment!
The skin is painted with the technique described in Vallejo's guide (except that I tried to preshade). Personally I think that dry brushing is good for ground, hair and fur.
The only place I "cheated" are the trousers, since black (more than white to me) is a bit a pain in the @ยงยง to me. So I dry brushed them with a very dark grey.
As for the mud you're right probably I should give it a wash of burnt umber or similar.