Asteroid Field

You create a 40-foot cube filled with drifting asteroids of all shapes and sizes, centered on a point within range. Each creature within the area when the asteroids appear must make a Dexterity saving throw. On a failed save, a creature takes 6d6 bludgeoning damage and is knocked prone. On a successful save, a creature takes half as much damage and isn't knocked prone. A creature must also make this saving throw when it enters the spell's area for the first time on a turn or ends its turn there.

A creature moving into or through the cube takes 1d6 bludgeoning damage for every 5 feet it moves, as asteroids violently collide with its body. A creature that can see the asteroids can avoid this damage by expending an additional 1 foot of movement for every foot it willingly moves within the cube.