The Hooked Shortspear can be found in Out of the Abyss, page 224.
An alchemical process has bonded silver to this magic weapon. When you score a Critical Hit with it against a creature that is shape-shifted, the weapon deals one additional die of damage.
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.