In The Witcher, Nivellen's curse is a result of his own misdeeds. He was coerced into violating a priestess of Coram Agh Tera by his squadmates, leading to him being cursed. The curse transformed him into a beast, but his mind and personality remained untouched. The curse was not an idle one, as it was cast by a priestess of the Lionhead Spider cult. The nature of the curse was such that Nivellen's physical form changed drastically, causing panic and confusion. However, he retained his memories and personality, leading to a unique existence where he was a beast in form but a man in mind. The exact way to lift the curse was unclear to Nivellen, with him only recalling something about 'love and blood'.