Shield of Cthulhu (5e Equipment)
From D&D Wiki
Armor (shield), rare (requires attunement)
A white oval shield with a jagged red rim and an open set of teeth in the center. While worn, you gain +1 to your AC; additionally, whenever you make the Dash action, you may choose to use this item to attack a single target within your movement range. When you do so, the target makes a DC 18 Dexterity save, taking 3d6 bludgeoning damage and being pushed back half of your remaining movement, rounded up, on a failed save, or 2d6 bludgeoning damage on a success.