Arctic Explosion

A glimmering light flashes from your finger to a point you choose within range and then explodes with the sound of glass shattering into an avalanche of snow and ice. Each creature in a 20-foot-radius sphere centered on that point must make a Constitution saving throw. A target takes 9d6 cold damage and has a 20ft reduction in their movement speed on their next turn on a failed save, or half as much damage and no movement speed reduction on a successful one. After this effect, the ground in the aforementioned radius is covered in slippery ice and sharp icicles. The area becomes difficult terrain for the duration. When a creature moves into or within the area, it takes 3d4 piercing damage for every 5 feet it travels.

The ice spreads around corners. It freezes water in the area for the next eight hours.

At Higher Levels. When you cast this spell using a spell slot of 7th level or higher, the blast damage increases by 1d6 for each slot level above 6th. When cast at 8th level or above, the icicles also deal 1d4 more damage.