Trident of the Electric Eel

Weapon (trident), uncommon (requires attunement)
  Imbued with the natural lightning-based magic of the eelfolk, this brass-headed, magical trident is enchanted never to succumb to the corrosive nature of the briny sea.
  Dinglehopper. As an action, you can command this weapon to magically shrink down to the size of common oyster folk, known as a dinglehopper, or to re-enlarge.
  Discharge. When you make a melee or ranged attack using this magic weapon you can speak its command word as a bonus action, causing it to emit a burst of lightning. Each creature within 5 f eet of it (or within 10 feet of it underwater), must succeed on a DC 13 Dexterity saving throw or take 1d6 lightning damage. A creature that fails this saving throw by 10 or more (DC 2) is also stunned until the end of its next turn.
  Lightning. As an action, you can cast the lightning bolt spell (save DC 13). Once you do so, you can’t use the Discharge or Lightning property again until the following dawn.
  Rare variant: The damage of Discharge increases to 1d10. The save DC of lightning bolt increases to 15, and the spell is cast at 5th level (10d6).
  Very Rare variant: The damage of Discharge increases to 2d6. Replace lightning bolt with chain lightning (save DC 16).