Battlecloaks and Torpor?
Battlecloaks essentially separate vampires into two groups - vampires without battlecloaks can't use most weapons to harm vampires with battlecloaks, and vice-versa. The difference between the two groups is that vampires with battlecloaks can be driven into Torpor (and, since they can damage other battlecloaked vampires, can also drive others into Torpor).
Hitting a battlecloaked vampire with garlic spray or a stake, or drinking their blood, when they have less than 10 blood remaining, will drive them into Torpor. A vampire in Torpor cannot attack vampires, nor use aggressive items, nor recover blood using necromancers. A vampire recovers from Torpor when they reach 250 blood.