Heldigslag, the Sling of Rolling Thunder

Weapon On a hit, the projectile explodes in a burst of electricity.  The wilder gets a bonus attack against a target within 15 feet of the original hit.  On a success, it deals 1d4 lighting damage.      The sling contains 2 small arcane jewels, one on each of its twin supports.  One contains a burst of Favor, granting one target within sight adavantage on a saving roll.  The other contains a burst of Hindrance, forcing one target's next saving roll to be with disadvantage.  The arcane energy can be recharged with a long rest.   Varies (this item requires attunement)