Thunder Barrier

You create a vertical wall of ligh, electricity and concentrated magical energy. The all appears within range and lasts for the duration. You can make a straight wall up to 50 feet long, 15 feet high, and 2 feet thick, or a ringed wall up to 30 feet in diameter, 15 feet high, and 3 feet thick. The wall provides three-quarters cover to creatures behind it, and its space is difficult terrain.

When a creature enters the wall's area for the first time on a turn or starts its turn there, the creature must make a Con saving throw. On a failed save, the creature takes 4d6 electricity damage. On a successful save, the creature takes half as much damage.