Acid Rain

An intense downpour of gelatinous, corrosive droplets appears in a 20-foot-radius, 40-foot high cylinder centered on a point within range, raining down on all below. Each creature in the cylinder when it appears and that ends its turn there must make a Dexterity saving throw, taking 6d6 acid damage on a failed save or half as much damage on a successful one.

In addition, if a creature takes 15 or more acid damage from this spell, then any nonmagical armor the creature is wearing takes a permanent and cumulative -1 to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. A mending spell can be used to restore these items to full functionality, at the rate of one casting of mending per -1 penalty