Given to Geralt by Regis as a token of appreciation after parting ways in Toussaint, Mutagenerator is a powerful item capable of storing life essence of dead beings killed by its wearer and then - when it is sufficiently charged - transmutates this energy into a random greater mutagen. This ability makes Mutagenerator a very useful item with regards to the mutation procedure discovered by professor Moreau and applied by Geralt.