Comet

You fire a great magical comet in a line 100 feet long and 5 feet wide. Each creature in the line must make a Dexterity saving throw. A creature takes 12d6 force damage on a failed save, or half as much on a successful one. If a creature that failed the save is Medium or smaller, it is knocked prone.
At Higher Levels.
When you cast this spell using a spell slot of 8th level or higher, the damage increases by 1d6 for each slot level above 7th.