This item appears to be a broken sword. While grasping the hilt, you can use a bonus action to cause a blade of pure darkness 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 Xarvia. Xarvia is a powerful sword forged by The Old Litch in a forgotten forge of the Shadowrealm. While attuned to Xarvia, you gain the following benefits.

You gain a +3 bonus to attack and damage rolls made with this weapon, which deals psychic damage instead of slashing damage. If you score a critical with it, the target has to succeed on a DC 18 Wisdom saving throw or be frightened of you for 1 minute. The target can repeat the save at the end of its next turns, with disadvantage if it's within line of sight of Xarvia. Undeads are immune to Xarvia's damage and abilities.

Whenever you deal damage to a creature with Xarvia, you can expend one of more or your Hit Dice to deal extra necrotic damage to the target. If you no longer have Hit Dice to expend, you can still roll them and substract the number rolled from your current Hit Points. Doing so reduces your maximum Hit Points by the same amount, this reduction lasts until you finish a long rest. These rolls also double if you score a critical hit (only for the damage against the target, not you).

Dark Magic. Xarvia can cast the following spells once per day each, it decides when to cast them and maintains concentration on them so you don't have to: hex, darkness, shadow of moil.

Descent Into Madness. When you kill a creature with this weapon, you can attempt to permanently twist its mind instead of killing it. If you do so the creature has to succeed on a DC 20 Wisdom saving throw or gain the following indefinite madness: 'I seek to please the shadows and I shall oppose the lightbringers'. If the creature succeeds the saving throw, it dies.

Umbral Requiem. If you summon Xarvia while being in dim light or darkness you can choose to summon it in its umbra form. In its umbra form, Xarvia's reach is increased by 5ft., and you roll 3d10 when rolling for damage instead of the normal damage rolls. If Xarvia is in its umbra form and you end your turn without attacking a creature, you have to succeed on a DC 18 Charisma saving throw, on a failure Xarvia takes complete control over your body. You can repeat the save at the end of your next turns, ending the control on a success. Xarvia's umbra form can only be ended if you die, if you end your turn in light or if you use your action to make a Charisma (Persuasion) check and roll an 18 or higher (you can use other Charisma-based skills for this check, DM's discretion).

Dark Harvest. When you use Xarvia to attack a target that is in dim light or darkness, you make the attack roll with advantage.

Soul Eater. Xarvia consumes the souls of all creatures it kills. A creature killed by Xarvia can only be revived by the use of a wish spell.

Sentience. Xarvia is a sentient chaotic-evil weapon with an Intelligence of 17, a Wisdom of 15 and a Charisma of 16. It has hearing and darkvision out to a range of 120 feet. The weapon communicates telepathically with you and can speak, read and understand Abyssal, Infernal, Undercommon and Common in addition to any language that you know.

Personality. Xarvia's purpose is to kill and devour souls, specially those of whom dare to opose it or its wielder. It thinks of itself as the most powerful weapon ever created, and as such, it only accepts to be wielded by a powerful warrior that meets its expectations. It will test anyone who tries to attune to it, and will reject those who it finds unworthy of its power. Xarvia's hunger for souls must be regularly fed. If this sword goes three days or more without consuming a soul, a conflict between it and its wielder occurs at the next midnight.

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, Replace Damage Type: Psychic, Weapon Property: Finesse, Damage, Control, Combat, Versatile, Sap