Here is the full list of all 12 Skin Witch achievements.
Beat the game on any difficulty.
Beat the game on Hard difficulty.
Beat the game on Nightmare difficulty.
Find all of the notes in a single playthrough.
Collapse a tunnel with explosives.
Become a mindless beast.
Achieve the normal ending.
Achieve the good ending.
Honor Kenneth's memory.
Create sacred herbs.
Incinerate a witch-beast.