Wondrous Item

Legendary Requires attunement by a creature missing its left arm Requires Attunement

When attuning to the arm, it attaches itself at the shoulder and can not be removed against the user's will until their attunement ends. The weapon arm is a fully functional body part. When inside an area without magic, it functions like a regular prosthetic.

Integrated Weapon: The arm comes with a pair of built in weapons: the Arm Cannon and the Arm Blade. Only one of these can be installed at a time and during a short or long rest the arm's user can change the currently installed weapon. When not in use, these weapons retract into the arm and are concealed. The user is considered proficient with these weapons.
Grapple Gun: The arm features an integrated grapple gun. As an action, the user can launch a grappling hook and cable to a point within 100 ft. The cable can support 3000 lb. Additionally, the user may make a special ranged attack against a creature up to one size larger than them within 30 ft. by making a ranged weapon attack roll against the target with the grapple gun (the user is considered proficient with the grapple gun). On a hit, the target is automatically grappled and can attempt to escape the grapple as normal on its turns. If the target is the same size as the user or smaller, it is pulled towards the user as far as possible. If the target is larger than the user, the user is pulled towards it as far as possible. The cable can be detached from the arm as a bonus action and takes one minute to reel back in for the grapple gun to be usable again.
Body Augmentation: The user's Str or Dex is increased by two. During a short or long rest, the user can change the augmented ability. Additionally, the user's AC is increased by one.

This onyx and gold prosthetic was commissioned by a legendary adventurer who had lost an arm and was dissatisfied with the prosthetic he had been provided. He sought out a master artificer and told him to create a prosthetic that would make him even more powerful than he was before.

Needless to say, he was very satisfied.