This item appears to be an adamantine dagger. While grasping the hilt, you can use a bonus action to cause a blade of incorporeal energy to spring into existence, or make the blade disappear. While the blade exists, this magic longsword has the finesse property. If you are proficient with shortswords or longswords, you are proficient with the Wraith Hunter.

You gain a +2 bonus to attack and damage rolls made with this weapon, which deals psychic damage instead of slashing damage. When you hit an undead with it, that target takes an extra 2d6 psychic damage.

After defeating and forcing several spirits to their final resting, an ethereal ornate crossguard also appears along with the extended blade when activated. You may now use Strength, Dexterity, or Charisma as your attack modifier and for your attack bonus. 

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage: Psychic, Replace Damage Type: Psychic, Weapon Property: Finesse, Bonus: Melee Weapon Attacks, Damage, Combat, Versatile, Sap