Caustic Strike

You brandish the weapon used in the spell's casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack's normal effects, and it becomes coated in corrosive acid. Until the start of your next turn, the target's AC is reduced by 1 due to the corrosive acid weakening its defenses.

At Higher Levels. At 5th level, the melee attack deals an extra 1d8 acid damage to the target on a hit, and the target's AC is reduced by 2. The acid damage increases by 1d8 at 11th level (2d8) and 17th level (3d8).