Regraftable Construct Arm (Patreon)

Wondrous item, very rare (requires attunement by a creature missing an arm)

This sickly flesh golem arm has been repurposed by a powerful necromancer, allowing it to be used as a prosthesis by any creature missing an arm. The prosthesis attaches to your arm at the shoulder, and it can't be removed as long as you're attuned to it. To attune to this item, you must hold it against your shoulder for the entire attunement period, at which point it magically sews itself into place. The arm detaches from you when your attunement to it ends.

Unarmed strikes made with the arm are considered magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage. While attuned it, your Strength score becomes 19 (unless it's already higher), and you have advantage on saving throws against any spell or effect that would alter your form.

Golem Spark. You can use a bonus action to allow the arm's necromantic magic to flood into you, granting you the following benefits for 1 minute. This property can't be ended early by any means. This property can't be used again until you finish a long rest.

• You have resistance to bludgeoning, piercing, and slashing damage from nonmagical attacks not made with adamantine weapons.
• Your unarmed strikes with the arm use a d8 damage die. A creature hit by an unarmed strike takes an extra 1d6 necrotic damage.
• You have advantage on saving throws against spells and other magical effects.
• Any lightning damage dealt to you is reduced to 0. When this happens, this property's duration is extended by 1 minute. The maximum remaining duration can't exceed 10 minutes at any time.

Curse. This arm is cursed, and attuning to it extends the curse to you. While you remain cursed, you must make a DC 15 Wisdom saving throw whenever you take fire damage. On a failed save, you spend your action on your next turn reeling and panicked. This saving throw can't be made with advantage. If you're under the effects of the Golem Spark property, you make this saving throw whenever you take any damage while you have less than half your hit points remaining. If you die while under the effects of Golem Spark, you immediately return to life with 40 hit points as a flesh golem. For the purpose of the golem's Berserk trait, your creator is the same as the arm's. Only a wish spell can return you to your original form.

"2 months of work! 50,000 gold in supplies! All right out the window! Let's hope I get more use out of this from you than I did from him."