I think I've got it:
Orc Champion's Belt
Wondrous item, rare (requires attunement)
This thick leather belt is fashioned from tanned dwarf skin. While wearing this belt, you gain the following benefits:
Reckless Attack. As a bonus action, you can gain advantage on melee weapon attack rolls using Strength until the end of your turn, but attack rolls against you have advantage until the start of your next turn.
Gruumsh's Blessing. When you reduce a hostile creature to 0 hit points, you gain temporary hit points equal to your Constitution modifier + your character level (minimum of 1).
Enmity of the Dwarves. While wearing this belt, you have disadvantage on all Charisma checks made to interact with dwarves.
Gruumsh's Curse. If you are not an orc, attuning to this belt causes Gruumsh to curse you for your insolence. Removing the belt fails to end the curse on you, and you cannot end your attunement to the belt until the curse is broken, such as with a remove curse spell.
As long as you remain cursed, you cannot benefit from Gruumsh's Blessing. In addition, whenever a hostile creature damages you, you must succeed on a DC 15 Charisma saving throw or go berserk. While berserk, you must use your action each round to attack the creature nearest to you with a melee attack. 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. You are berserk until you start your turn with no creatures within 60 feet of you that you can see or hear.
Comments:
I see you made it overtly cursed. Personally I think I prefer items which avoid this mechanism, and instead offer "advantages" that are so inherently ambivalent as to be a sufficient deterrent in themselves.
Reckless attack: Having to spend a bonus action each round is a significant drawback. Do note Barbarians don't have this cost. This makes this benefit of questionable utility. I'm guessing you would have to think hard about when and where you use this ability (which thematically is kinda the opposite of "reckless"...) If opponent AC is low, there are many enemies and/or the foes are individually weak, you would be better off making three attacks instead of two. If opponent AC is high, the "advantage of advantage" quickly tapers off. I would consider removing the bonus action cost, and simply duplicate the Barbarian ability. Alternatively: add Orc-flavored utility to that bonus action, such as:
Reckless aggression: You can spend your bonus action on reckless aggression. This allows you to move up to your speed towards a hostile creature you see. It also gives you advantage on melee weapon attack rolls using Strength during this turn, but attack rolls against you have advantage until your next turn.
This way, the cost of using your bonus action is mitigated by an uniquely orcish benefit. Do note you can still do "reckless aggression" even if you don't want to move anywhere.
Gruumsh' Blessing: good to go
Enmity of the Dwarves: I have always thought leaving the attitude of NPCs up to random rolls (as per the DMG rules) to be wonky. If my player wore this and met a couple of Dwarves, I would decide they would not have anything to do with this character, no rolls needed (or allowed). I guess I would re-phrase this to "The attitude towards you and your allies, of any Dwarf you encounter, switches automatically to Hostile when and if he or she sees you wearing this belt". This wording would make it clear to the player what to expect with me as the DM
Gruumsh' Curse: Consider keeping only the berserker bit. That is, something like this:
Gruumsh' Wrath: Once a round, when a hostile creature damages you, you must succeed on a DC 15 Charisma saving throw or go berserk. While berserk, you must use your action to attack an adjacent creature with all available melee attack(s), dealing 1d8 extra damage with every hit. If no creatures are adjacent, you must move adjacent to the creature nearest to you. If you have multiple possible targets, you attack one at random. At the start of each of your turns, if no creatures you see or hear are within 60 feet of you, or if you make a DC 15 Charisma save, you stop being berserk.
This is based on the notion that berserking isn't a curse to a proper Orc Chief
