Brushes, Prints & Workshops -> https://www.arsfantasio.de
This one is a demo piece on how to paint creature skin based on a creature design from Aris Kolokontes and a photo reference for the Glasses / hair.
Since it is an extreme example, if you can master this, the result can easily applied to retouch and painting human skin as well.
I usually teach methods in my (RL) classes so I don't know if someone gets something out of this demo.
However, you can get the brushes or the brushes and video material on Gumroad here:
And just the Brushes: