This item appears to be a longsword hilt. While grasping the hilt, you can use a free action to cause a blade of pure 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 Xenosith's lightsaber.

You gain a +3 bonus to attack rolls and 1d10+3 bonus damage rolls made with this weapon which deals force damage instead of slashing damage. 

The sword's luminous blade emits bright light in a 15-foot radius and dim light for an additional 15 feet. 

This weapon has the thrown property with a range of 45/120

Destroy Weapons. You gain the ability to parry while attuned to this weapon, as a reaction add 3 to your AC against a single melee attack that would hit you. Any nonmagical weapon that hits the Xenosith's lightsaber is damaged. After dealing damage, the weapon takes a permanent and cumulative −2 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed. This doesn't effect natural weapons.

Corrode Armor.  If the object touched is either armor or a shield being worn or carried, it takes a permanent and cumulative −2 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. This doesn't effect natural armor.

Energy Absorption. Whenever you are targeted by a spell that deals lightning or force damage and requires you to make a Dexterity saving throw, you gain advantage on the save, and on a success take no damage. As well on a success roll a d6. 1-5 and you gain a spell slot equal to half the spell's level rounded down. 6 you gain a spell slot equal to half the spell's level rounded down and reflect the spell back at the caster as if they were the target.

Dismember. On a natural 20 you deal an extra 3d8 force damage and remove a limb or appendage of the DMs choice. On a natural 1-3 roll a DC 20 Dexterity saving throw, on a failure you take 3d8 force damage and lose an appendage of the DMs choice. On a success take half damage and you do not lose a limb.

Lightsaber vs Magic. Whenever the lightsaber strikes a magic item, or magical terrain the item must make a DC 15 Constitution saving throw. The item receives a bonus dependent on it's rarity; Common +1, Uncommon +2, etc. unless the object has a Constitution score of its own. On a failure the struck item takes the same penalty as described in the corrode armor and destroy weapons features. Legendary items and Artifacts are immune to this effect. Two attacks with this weapon dispels a wall of force. This blade can't cut through adamantine, zardazik, celestial steel, infernal iron, and a few other materials. Cutting through a nonmagical stone door takes 10 minutes for a hole large enough for a medium or smaller creature per 5 feet of thickness.

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: Force, Weapon Property: Finesse, Weapon Property: Thrown, Damage: Force, a spellcaster, Damage, Combat, Versatile, Sap