One of my favorite aspects of the Tomb Kings was converting all the skeletal horses, including those pulling the chariots. I believe it was either the cover of the new army book or one of the interior illustrations that showed the horses with these scale mail 'blankets'.
I could not resist trying to make those myself! I even had to create an entire theme/story to go with them :-)
I used tin foil as a base for the green stuff, which could be pressed into a mould (made from the original piece that I sculpted) and then wrapped over the miniature. This tin foil gave the green stuff critical support as it cured, so I could put the blankets into any position that I wanted, and it would not sag!
I also had a lot of fun with the "demon marble"... so much fun that I even made one of my kickstarter painting videos featuring this technique. The entire army was painted with this marble effect.
You can get a better view of that here:
Here's an example of converting the Hierophant on skeletal horse:
One last view of an old favorite!