War Pick of Corrosion (Patreon)

Weapon (war pick), very rare (requires attunement)

This weapon resembles the head of an ancient black dragon: its two horns curl behind its head to form the weapon's sharp pick. You gain a +2 bonus to attack and damage rolls made with this magic weapon, which deals an extra 1d4 acid damage to any target it hits. This extra acid damage is doubled if the target is made of metal or is wearing metal armor.

The weapon has 5 charges and regains all expended charges daily at dawn. Once on each of your turns when you hit a target with the war pick, you can expend 1 of its charges to increase the pick's acid damage by 3d4, to a total of 4d4 extra acid damage. If the target is wearing armor, it must also succeed on a DC 16 Constitution saving throw or take a cumulative −2 penalty to its armor class, to a minimum of 10 AC, which lasts until it finishes a short or long rest.

"I swore an oath of revenge. To stop at nothing, and no one, until they, too, knew my pain. So: do you truly believe that your meager wall of armor will stand in my way?

"No. I thought not."