Corrosive Jab

As part of the action used to cast this spell, you must make a melee attack with a weapon or an unarmed attack against one creature within the spell's range, otherwise the spell fails. Your weapon becomes sheathed in an acid capable of melting the toughest armors and hides. After a successful hit, roll 1d4. Subtract the roll from the target’s current AC. This total replaces their AC until the beginning of your next turn. 

This spell’s damage increases at higher levels. At 5th level, your melee attack deals an additional 1d8 acid damage.The damage increases by 1d8 at 11th level and 17th level.