Oh my goodness, I know that feeling of that darn fused shadow ORT.
I cosplayed Midna back in 2010. For the fused shadow I drafted out a pattern and cut the shapes using that foam.. paper stuff?
Ah, Foam Sheets. I bought mine at Michaels and it came in a roll like THIS
except it was white.
One of your pieces should be the bowl that you will place around your head. It must be TIGHT but not too tight so you dont hurt your head and ears.
The other piece will be the front piece with the snakes on it.
You may need to cut extra pieces to add to certain areas for more thickness.
For the snakes and the eyes I hand crafted them out of white Model Magic clay and hot glued them on to the foam sheet parts. The cracks and designs I drew on with Scribbles Fabric Paint that I also bought at Michaels.
Of the over-all 'stone' color, I used two different spray paints. A Grainy Grey (that is supposed to resemble rock) and a brown-green color.
Here is what my headpiece looked like~
Yikes. There are definitely some things I'd change about my Midna cosplay if I were to redo it, but I've since retired this costume
I recommend using thicker foam sheets then I did, to make it look more 3D and 'real'. Just make sure you're able to bend it well.
Good luck! Please message me if you have any more questions and I'd love to see the finished product you come up with. I hope my tips helped~