Metallurgist's Grip (Patreon)

Wondrous item, very rare (requires attunement)

This plated metal gauntlet extends up your arm. The armored plates are extensively corroded. If you're missing a hand or arm, the item can function as a prosthesis for it. While you're attuned to the gauntlet, it can't be removed from you against your will, and you have resistance to acid damage.

While wearing the gauntlet or using it as a prosthesis, you gain the following properties.

Absorb Acid. You can use your reaction whenever you take acid damage to reduce the acid damage you take by 2d6 + 3. When you do, the next melee weapon attack you make before the end of your next turn deals extra acid damage equal to the acid damage it reduced.

Caustic Overdrive. You can use a bonus action to cast the haste spell on yourself from the gauntlet. When you do, the spell doesn't require concentration, and you must roll a d6 at the end of each of your turns. You take acid damage equal to the result of the d6, which can't be prevented or reduced in any way. On a 1, the spell ends. Once this property has been used, it can't be used again until the next dawn.

The wizened mage ran steel fingers along the ore, feeling out the give and heft. Though the gauntlet he wore was long empty—its hand long lost to youthful intemperance—he felt the fire in his shoulder as he probed the metal's secrets.

Of those was its rapidly dwindling heat, doomed to fade long before his aging hands could shape it.

His teeth set; despite its cost, haste here was worth the toll. Toxic pain seized him, agony driving his hammer-like fist ever faster against the metal to twist it into a half-formed blade. To any other the wild pace would be beyond control, but by his skill and speed, the shape of something masterful emerged.

His fingers still tingled and burned from the corrosive hunger, but they wrapped proudly around the newly-birthed sword. He plunged it into an acrid bath. As the final treatment's pungent steam rose around him, he finally allowed the lethargy to take hold of him, and the arm hung limply from his shoulder.