Soulsword

Weapon (longsword), legendary (requires attunement)
  The Soulsword is a unique blade once possessed by Strahd’s brother, Sergei von Zarovich. In its original form, it had a platinum hilt and guard, and a thin crystal blade as strong as steel.
  Now, all that remains is the longsword's ornate hilt. While grasping the hilt, you can use a bonus action to cause a blade of pure radiance 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 Soulsword.
  You gain a +2 bonus to attack and damage rolls made with this weapon, which deals radiant damage instead of slashing damage. When you hit an undead creature with it, that target takes an extra 1d8 radiant damage.
  The sword's luminous blade emits bright light in a 15-foot radius and dim light for an additional 15 feet. The light is sunlight. While the blade persists, you can use an action to expand or reduce its radius of bright and dim light by 5 feet each, to a maximum of 30 feet each or a minimum of 5 feet each.
  Spirit of Vengence. When you attune with the Soulsword, it gains charges equal to the attuned creature's spellcasting modifier; these charges regenerate at dawn. When you hit a creature with a melee weapon attack, you can expend charges to deal additional radiant damage to the target. The extra damage is 2d8 for the first charge, and then 1d8 for each addition charge.
  Resplendent Soul. When you are attuned with the Soulsword and you deal radiant damage to a creature, you can choose any willing creature touched by the light of this sword's luminous blade and they gain temporary hits points equal to the total radiant damage dealt.
  Sentience. The Soulsword is a sentient chaotic good weapon with an Intelligence of 11, a Wisdom of 17, and a Charisma of 16. It has hearing and normal vision out to a range of 60 feet. The weapon communicates by transmitting emotions to the creature carrying or wielding it.
  Personality. The Soulsword's special purpose is to destroy Strahd, not so much because it wants to free the land of Barovia from evil but because it wants revenge...
Item type
Weapon, Melee