The standard challenge rating for a vampire is 13.
Some vampires have undergone martial arts training and possess battlefield experience. In this case, a vampire warrior dressed in plate armor and wielding a greatsword would have a challenge rating of 15. Additionally, some vampires were once followers of arcane secret techniques, which also increases their challenge rating.
Leon stared at Envis. From Envis's complexion, he could tell that Envis was a vampire.
Looking closer, Envis was fully armed, wearing plate armor and holding a longsword, with the ability to control a Zombie Dragon. It was clear that Envis was a rare magic-and-martial dual cultivator vampire, not just skilled in combat but also a powerful spellcaster. Leon was sure that Envis was stronger than the Death Knight he had encountered before.
