In Beast's Clothing is a book in The Witcher 3: Wild Hunt that, when read, provides bestiary entries for werewolves and ulfhedinn, as well as the formula for werewolf decoction.
A copy of it can be received as a reward for the unmarked quest Man's Best Friend, and it can be purchased from Marcus T.K. Hodgson or the books merchant in Hierarch Square. It should also be available as random loot, but due to a randomization bug can only and always be found at the bandit camp north of the Forest Hut in Spitfire Bluff.
Journal entry[]
- They entered his hut and began to search. First they tore through his bed. Dried twigs covered the sheet - that was the first proof, for werewolves return at dawn after a night of hunting, their bare feet covered in the forest's droppings. They found the second proof under his bed: a wolf's hide. The werewolf surely dressed himself in it when transforming with the setting sun, and shed it again when he turned to man the next day. Having found these powerful proofs they ceased deliberation and began the hunt, vowing to find the lycanthrope and bind him in silver chains.