Weapon of Berserk Fury

Melee weapon, rare, requires attunement by barbarian

In the hands of a non-barbarian, you gain a +1 bonus to attack and damage rolls made with this magic weapon.

In the hands of a barbarian, however, the weapon awakens to its full power. You gain a +1 bonus to attack and damage rolls. In addition, while you are attuned to this weapon, your hit point maximum increases by 1 for each level you have attained.

Curse. This weapon is cursed, and becoming attuned to it extends the curse to you. As long as you remain cursed, you are unwilling to part with the weapon, keeping it within reach at all times. You also have disadvantage on attack rolls with weapons other than this one, unless no foe is within 60 feet of you that you can see or hear.

Whenever a hostile creature damages you while the weapon is in your possession, you must succeed on a DC 15 Wisdom saving throw or go berserk: While berserk, you must use your action each round to attack the creature nearest to you (friend or foe) with the weapon. If you can make extra attacks as part of the Attack action, you use those extra attacks, moving to attack the next nearest creature after you fell your current target. If you have multiple possible targets, you attack one at random, though you may prioritize hostile creatures over friends and allies.

You are berserk until you start your turn with no creatures within 60 feet of you that you can see or hear. If you have only non-hostile creatures within 60 feet of you, you may attempt to come out of the berserk state by making a DC 15 Wisdom saving throw, but the DC modified by a +1 for each creature slain during your berserk state.

Close friends and allies may spend an action on their turn trying to "talk you down", and give you another saving throw attempt. The DM may give advantage or disadvantage on the roll depending on the nature of the relationship to you and the friend or ally trying to "talk you down".