Shield of the Eldritch Maw

Armor (shield), very rare

The face of this shield is seemingly made of teeth, with a clear, fanglike line through its center. While holding this shield, you have a +2 bonus to AC. This bonus is in addition to the shield's normal bonus to AC.

Whenever a creature makes a melee attack roll against you while you're holding the shield, you can use your reaction to make a special melee attack with the shield against that target, with an attack bonus of +8. When you do, the shield splits apart to form a toothy maw, which opens wide and bites down on the target. On a hit, the target takes 1d4 piercing damage plus 1d6 psychic damage. If you roll a 20 on the attack roll, the target is magically shunted to a special demiplane within the shield. The creature remains in the demiplane until you end the effect (no action required) or until you doff the shield, to a maximum of 1 minute, during which time it takes 1d4 acid damage plus 3d6 psychic damage at the end of each of its turns. A creature reduced to 0 hit points in the demiplane is devoured. At the start of each of its turns, the shunted creature can make a DC 16 Charisma saving throw. On a successful save, it escapes the demiplane and reappears in the nearest unoccupied space to the shield. Only one creature can be in the demiplane at a time.

Nine out of ten aberrations recommend brushing twice a day and flossing to remove those pesky, stuck-in monster parts.