Mechanical Quarterstaff of Power (5e Equipment)

Weapon (quarterstaff), Legendary (requires attunement by a warforged) A mysterious staff made from a mysterious super alloy. It’s user can control all metal and partly make things decay. To attune to this item, you must hold it against your arm for the entire attunement period. As a bonus action, you can retract the quarterstaff into your arm or draw it from there. This quarterstaff deal 2d10 damage, instead of the normal damage, when attacking with one hand, or 3d8 additional damage when attacking with both hands. The damage type can be either bludgeoning or slashing, you must make the choice when you take the Attack action. In addition, regardless of the way you choose to attack with this quarterstaff, you deal additional 1d8 necrotic damage.