Thalassic Tincture

Potion, very rare

This concentrated essence of the ocean’s salty waters causes metals to rust on contact and is usually stored in wooden or leather containers.

As an action, the thalassic tincture can be poured on a stationary metal object, causing it to take 8d6 acid damage as it begins to rust away. If the object is a metal shield or armor, its AC bonus is permanently reduced by 1 each round until the armor or shield is doused in oil or treated with universal solvent, which neutralizes the thalassic tincture. If this reduces it to AC 10 (+0 for a shield), the item is destroyed. Weapons similarly take a permanent -1 penalty on damage rolls each round, and if they reach -5 the item is destroyed.

A bottle of thalassic tincture can be thrown as an improvised weapon, exploding in a breaking wave of extreme salinity. The target takes 2d6 bludgeoning damage (plus 2d6 acid damage for a creature or object made of metal) on a hit and must succeed on a DC 13 Dexterity saving throw or be knocked prone by the surging water, with any metal armor shield it is wearing reduced in AC by 1 as above; this reduction does not increase on later rounds. Creatures adjacent to the target take 1d6 bludgeoning damage (plus 1d6 acid damage for metal objects and creatures) or half as much with a successful DC 13 Dexterity saving throw, and creatures failing their save are pushed 5 feet away from the target.

A hurled thalassic tincture deals damage to fire-using creatures (GM’s discretion) as if they were metal creatures, and non-magical fires in the splash area are automatically extinguished while magical fires are affected as dispel magic.