Sculpt, then bake
If the body is big, I crunch up aluminium foil to fill the central void, so the polymer clay is no more than half an inch thick. I use glass beads for eyes, or sometimes glass animal eyes from a taxidermy supplier. I sculpt only the part of the animal above the mud, and the cracked-mud texture around it. I harden the sculpt by curing it in the oven.
Baked in oven at 275 degrees for 15 minutes to cure Thin layer of Sculpey over plywood base
Black glass eyes