You gain a +1 bonus to attack rolls and damage rolls made with this magic weapon. 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.
Whenever another creature damages you while the weapon is in your possession, you must succeed on a DC 15 Wisdom saving throw or go berserk. This berserk state ends when you start your turn and there are no creatures within 60 feet of you that you can see or hear.
While berserk, you regard the creature nearest to you that you can see or hear as your enemy. If there are multiple possible creatures, choose one at random. On each of your turns, you must move as close to the creature as possible and take the Attack action, targeting the creature. If you’re unable to get close enough to the creature to attack it with the weapon, your turn ends after you’ve used up all your available movement. If the creature dies or can no longer be seen or heard by you, the next nearest creature that you can see or hear becomes your new target.
Proficiency with a Greataxe allows you to add your proficiency bonus to the attack roll for any attack you make with it.
This weapon has the following mastery property. To use this property, you must have a feature that lets you use it.
Cleave. If you hit a creature with a melee attack roll using this weapon, you can make a melee attack roll with the weapon against a second creature within 5 feet of the first that is also within your reach. On a hit, the second creature takes the weapon’s damage, but don’t add your ability modifier to that damage unless that modifier is negative. You can make this extra attack only once per turn.
Notes: Bonus: Magic, Bonus: Hit Points per Level, Combat, Cursed, Heavy, Two-Handed, Cleave
What is the attunement requirement.
And do you go berserk once someone takes your axe
I would rule since the cursed creature is unwilling to part with it, there would be a contested strength check. But should it be stolen or forcibly taken they would need to roll the wisdom saving throw or go berserk. Either way unless a remove curse or similar is used on them I would say the affected character would do what they could to get it back.
Typically unless the notes say otherwise it takes at least a short rest familiarizing themselves with the item. In this example perhaps spending the short rest working through movements with the weapon learning the feel.
I would use this for my Melee Ranger, but the curse is to detrimental…