Behind the Great Veil is a book in The Witcher 3: Wild Hunt that, when read, provides bestiary entries for wraiths and hyms, as well as the formula for wraith decoction.
It should be available as random loot, but due to a randomization bug can only and always be found in a chest inside the library during The Tower Outta Nowheres.
Journal entry[]
- Of the many demons which reside in the outer spheres, hyms are among the most dangerous. Other demons usually must take on concrete living form - be it of man or beast. Hyms, on the other hand, appear in our world in their own immaterial form, which is invisible to all save their chosen victim.
- Hyms feed on fear, regret, a sense of guilt - in a word, on negative emotions, and since they are eternally hungry, they provoke these emotions in the humans they torment. These demons cannot be exorcized. A man a hym takes as a victim is lost and will inevitably succumb to madness, and then death.