Chain Enervation

You fire a bolt of negative energy at one creature you can see within range.  Make a ranged spell attack.  On a hit, the target takes 12d6 necrotic damage and the creature must succeed a Constitution saving throw or gain a level of exhaustion.  The bolt then leaps to another target of your choice within 60 feet of the first that hasn't already been affected by this spell.  The blast continues to chain until there are no more targets within its reach or the spell attack roll misses.