Source: Bigby Presents - Glory of the Giants

Armor (Breastplate), Legendary (Requires Attunement)

This breastplate is made from marbled granite, though it feels no heavier than a typical metal breastplate. Its chest is emblazoned with the stone rune.

While wearing this breastplate, you have resistance to bludgeoning, piercing, and slashing damage and are immune to being knocked prone.

Invoking the Rune. As an action, you can invoke the breastplate’s rune to cast the Wall of Stone spell (save DC 14) with it. When you cast the spell in this way, you have advantage on saving throws made to maintain concentration on the spell.

Once the rune has been invoked, it can’t be invoked again until the next dawn.