Dragon's tooth

You create a vertical wall of whirling, razor-sharp blades made of magical energy. The wall appears within range and lasts for the duration. You can make a straight wall 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 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 dexterity saving throw. On a failed save, the creature takes 6d10 slashing damage. On a successful save, the creature takes half as much damage.