Ghost Fang

Magic Item Type: Weapon (Dagger)
Rarity: Legendary
Requirements: Attunement by a character that is not undead
Description: The Ghost Fang is a silver-plated dagger, bestowed with everbright and blueshine enchantments, making it immune to tarnishing and acid damage. It is a +3 dagger of vampire slaying, feared by vampires far and wide.

Properties:

Vampire Awareness: Vampires within a 6-mile radius can sense the presence of The Ghost Fang. They are compelled to seek out and destroy the bearer or force them to dispose of the dagger by any means necessary.
Wraithform: The bearer can use an action to assume wraithform at will, resembling a drifting or flying ghost. This form grants the benefits of the gaseous form spell, but the bearer can still hold, use, and interact with objects as normal.
Vampire Slaying: On a hit against a vampire, the dagger deals an extra 1d4 piercing and slashing damage (for a total of 1d4 + 3 + ability modifier damage). Instead of killing the vampire, it transforms them into a zombie. This transformation is permanent, causing the vampire to lose all vampire abilities, lair actions, and vulnerabilities, and instead gain the powers and abilities of a zombie.
Evasion: If ever touched by a lich or struck by a hostile necromantic spell of 6th level or higher, The Ghost Fang vanishes. It teleports spontaneously to a random location in Faerûn, where it may be found by anyone.

Origin: 

The origins of The Ghost Fang are shrouded in mystery. Some say it was created by an elf on Evermeet about 1200 years ago, while others argue it was the work of dwarves from an ancient clan. Its tendency to change hands frequently is well-documented, partly due to its self-preservation mechanism against necromantic forces.