Source: Eberron - Rising from the Last War

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

This prosthetic appendage was developed by artificers of House Cannith. To attune to this item, you must attach it to your arm at the wrist, elbow, or shoulder, at which point the prosthetic magically forms a copy of the appendage it's replacing.

While attached, the prosthetic provides these benefits:

• The prosthetic is a fully capable part of your body.
• You can take an action to remove the prosthetic, and it removes itself if your attunement to it ends. It can't be removed against your will.
• The prosthetic is a magic melee weapon with which you're proficient. It deals 1d8 force damage on a hit and has the thrown property, with a normal range of 20 feet and a long range of 60 feet. When thrown, the prosthetic detaches and flies at the target of the attack, then immediately returns to you and reattaches.