Armor of Corrosion

You touch a creature, causing their body to be enveloped by a flexible, semi-solid acidic liquid that protects them like armor. For the duration of the spell, the target's AC cannot be lower than 17, it gains immunity to Acid damage, and it gains advantage on Ability Checks meant to escape grapples.

Any creature or object that touches the armor takes 2d4 Acid damage, including when the wearer of the armor attacks and hits a foe with a melee attack. Any spell or cantrip that deals Acid damage (not including this one) cast while enveloped in the armor is cast as though it was 1 level higher, or else deals an extra die of damage.