looking for a book i read about 20+ years ago
The book’s story is set in a fantasy world The main character is a human boy whose father cut his arm off because local priests predicted some boy missing an arm would arrive and have it fixed with a magic one they had to attach on and fulfill some prophecy
the boys companions are his vampire girlfriend and a barbarian girl whose skin is turning to stone.
only read partway in, the part of the plot I can remember is the group are fleeing an evil brother/sister sorcerer couple who are trying to stop the boy from fulfilling the prophecy
The cover of the book had the boy touching some artifact that was burning his hands, his vampire girlfriend covering her face and barbarian girl just watching