Your going to call me crazy. However. Paint all the skin grey. Then paint all the recesses etc a bright blue. Then drybrush with a darker grey and touch up anywhere where you have gone over with the blue. Next apply a heavy nuln oil wash. It will auto highlight the mandrake nicely. Then once it has dried try and fill in the blue recesses again.
Mandrakes are fiddly work, but perhaps try that, washes make everything easier! If it is too bright drybrush it with black and hey presto, a less troublesome mandrake! Merry Xmas as well!
Delicious and Coven-Baked for your Pleasure
A very slow, 30K Salamander Distraction Log: VULKAN LIVES