Blade Barrier

You create a vertical wall of whirling, razor-sharp blades made of magical energy. The wall can be up to 100 feet long, 20 feet high, and 5 feet thick, or a ringed wall up to 60 feet in diameter, 20 feet high, and 5 feet thick. The wall provides three-quarters cover, 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, it must make a Dexterity saving throw, taking 6d10 slashing damage on a failure, or half on a success.