Cheers again for the comments, guys! They really keep me going!
There will be a third party representing the 'force of Mother Nature'...
Am I right in thinking you've based it on a Limax maximus or otherwise more commonly known as a Leopard Slug... 

I have thought of researching the correct common term for that species but thought it too time-consuming. Here in Germany, it is oddly enough called '
Tigerschlegel' - Tiger Slug.
We have some of them in out garden-real ones, I mean...

I am sitting in front of my pc with a huge smile on my face and I still can't wrap my head around the project's brilliance! Sometimes in hobby life there are moments of blinding cheerful creativity that makes you think: "That's why I am doing this!"... Thank you for giving me one of those moments.
@Remington and Hazel: This really is a nice thing you said. Cheers!

Luckily, Welf VIII. from this forum requested some in-progress shots while I painted the miniature, so I can show you how I did the rust effect on the skeleton's armour:
VGC=Vallejo Game Colour
VMC=Vallejo Model Colour
I always thin my paint with a 1:6 Mixture of Water/Future Floor Wax.
Step 1:
Metal parts primed white(!) sprayed over a black undercoat. I find it easier to define the general direction of light shining on the miniature.

Step 2:
VMC #828 Woodgrain (Transparent) wash over metal parts:

Sorry for the blurry pic...
Step 3:
First highlight using a 50/50 mix of VMC #828 and #851 Deep Orange. I applied the mixture as a wash. The trick with rust is that it works the opposite way that other materials. Liquids tend to collect in the deepest areas of a metallic object, so the lightest parts should be in the recesses. So it really should be called 'deeplight'...

Curses! Blurryness again!!!

Step 4:
I added some more orange to the mix and applied it to smaller areas deeper in the recesses:

Step 5:
Some VGC #38 'Scrofulous Brown' to give it a yellowish hue and VVMC #70815 'Basic Skintone' to make it more opaque was added into the mix:

...and a different view:

Step 6:
I added some metal areas where the rust has chipped off in order to break up the whole, erm, orangyness. I used VGC #54 Gunmetal and VGC #72053 chainmail for this:

Done!
This is far too time-consuming and over-the-top for a simple gaming piece, but it had to be done, don't you think?