You gain a +2 bonus to attack and damage rolls made with this magic weapon.

In addition, while attuned your hit point maximum increases by 2 for each character level (up to a total of 20). The hit points only remain while you are attuned to this magic weapon.

Curse. This sword is cursed and possessed by a vengeful spirit. Becoming attuned to it extends the curse to you. As long as you remain cursed you are unwilling to part with the sword, keeping it on your person at all times, and will stop at nothing to get it back. While attuned to this weapon, you have disadvantage on attack rolls made with weapons other than this one.

In addition, while the sword is on your person, you must succeed on a DC 15 Wisdom saving throw whenever you take damage in combat. On a failed save, you must attack the creature that damaged you until you drop to 0 hit points or it does, or until you can’t reach the creature to make a melee attack against it. During that time, if you score a critical hit against this creature, it takes an additional 10 slashing damage. You have advantage on saving throws from this creature against its spells and illusions, and are immune to being charmed by it. 

You can break the curse in the usual ways, but requires a caster of level 9 or higher.

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, Bonus: Hit Points per Level, Combat, Cursed, Versatile, Sap