Slumbering Dragon's Wrath Sword

Weapon

Uncommon Must be attuned Requires Attunement

Slumbering (Uncommon). Whenever you roll a 20 on your attack roll with this weapon, each creature of your choice within 5 feet of the target takes 5 damage of the type dealt by the dragon’s breath weapon.

Source: Fizban's Treasury of Dragons
Weapon (Any), Rarity Varies (Requires Attunement)

This weapon is decorated with dragon heads, claws, wings, scales, or Draconic letters. When it steeps in a dragon’s hoard, it absorbs the energy of the dragon’s breath weapon and deals damage of that type with its special properties.