Tempest Whetstone

Sharpened by the Tempest. This whetstone has a total of 1d8 uses. You can use an action to use the whetstone on one melee weapon or piece of ammunition that deals Piercing or Slashing damage. For the next minute, the item deals an additional 4d6 Lightning damage when you hit a creature with it. On a critical hit, the target also must make a Constitution saving throw (DC 16). On a failed save, they are Stunned until the start of their next turn. A weapon can only be empowered with this whetstone once per day, and it can be empowered again after the next dawn.