Longtooth’s Trinket

This trinket is a token from the Beaversfolk tribe, especially from Longtooth the Eldest.
As a bonus action, this trinket allows the attuned wielder to coat themselves in a suit of thick wooden armor, granting them 20 temporary HP and resistance to Bludgeoning and Piercing damage, but vulnerability to fire damage.
Once the temporary hit points are gone, the armor shatters dealing 1d6 piercing damage to all other creatures within 5 feet.
Once used this feature is not available again until after a long rest.

We got this item after saving The Dome in session 23 - Heavens' Outcasts.