When a Vampire, or other undead with a blood-drinking like ability, makes a successful Bite attack, the effects are inverted. The Anti-Vamp reduces all damage from the attack to 0, and instead causes the Creature to take the damage instead, replacing Necrotic with Radiant damage. The Anti-Vamp then heals for an amount equal to the damage dealt, gaining temporary hit points for any above their Hit Point Maximum.

When an Anti-Vamp is targeted by a Vampires Charm ability, it reflects the effects onto the creature. The Vampire must make a saving throw vs. it's own Wisdom Save for the ability, or be Frightened by the intended target. This effect lasts until the vampire succeeds on another Saving throw (using the same DC) after taking damage from any source, or after 24 hours. 

An Anti-Vamp is able to detect the presence of any vampires or their minions within a 100 ft radius. Only the presence is detected, not the number or type of creature. If a Vampire or it's minions are within 15 ft, the Anti-Vamp can detect whether a creature is a Vampire or a minion on a successful DC12 Wisdom check. 

the Anti-Vamp gains Proficiency with Will Saves, as well as a +1 to both Wisdom and Constitution scores.