Skull - from Creature Box concept to Zbrush

Based on Creature Box concept (kudos for inspiration), this is my take for Zbrush Central Italy speed sculpt weekly challenge.
Since I'm still learning Zbrush ( It's been some months now, and still I need to understand it) I'm leaving aside the speed part, and focusing on learning the effects of brushes & techniques.
It took me 4 hours to sculpt & 1 hour to paint + PS compositing