Shellcracker

Through tactical positioning, you manage to make a strategic move leaving an opening against an heavily armored or shielded target. This attack is made with +8 to hit instead of its normal bonuses. If the target is struck, it suffers no damage. If the target has an AC of 20 or higher, or is wielding a shield, its AC is instead sundered by an amount equal to 1d4 for 1d4 rounds. At the end of this effect, the targets AC returns to normal. This feat may not be used again until you finish a short or long rest.