Ubtao's Storm Cage

A 20x20 foot cage of pure lightning forms into existence centered on a point you choose within range. The cage remains for the spell’s duration. Each creature in the cage when it appears, passes through the cage's boundaries, or that ends its turn there must succeed on a Constitution saving throw or take 2d6 Thunder damage. The Cage’s space is difficult terrain.  

Until the spell ends, you can use a bonus action on each of your turns to cause a bolt of lightning to leap from the  cage toward one creature you choose within the cage. Make a ranged spell attack. . On a hit, the target takes 6d6 lightning damage.

Creatures within 30 feet of the cage have disadvantage on Wisdom (Perception) checks made to listen.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the damage increases for each of its effects by 1d6 for each slot level above 5th.