Shimmering Shield (5e Equipment)
From D&D Wiki
Armor (shield), rare
A metal shield that has shimmering flecks embedded into its face.
The shield can hold four charges. When you are hit with a melee attack, you can spend a charge to force the attacker to make a DC 14 Dexterity saving throw. On a failed save, the attacker takes 1d8 force damage as a small shockwave bounces out of the shield. The shield regains 1d4 charges at dawn.
When the last charge is spent, roll 1d20. On a 1, the shield shatters, and deals an extra 1d8 force damage to the attacker on an unsuccessful save.