The Hooked Shortspear can be found in Out of the Abyss, page 224.
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.
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.
On a hit with this weapon, the wielder can forgo dealing damage and attempt to trip the target, in which case the target must succeed on a Strength saving throw or fall prone. The DC is 8 + the wielder's Strength modifier + the wielder's proficiency bonus.
A light weapon is small and easy to handle, making it ideal for use when fighting with two weapons.