Aganazzar’s Scorcher (revised)

You draw a line of roaring flame on a solid surface within range. The flames take the shape of a Line that is 30 feet long and 5 feet wide. Each creature in the area must make a Dexterity saving throw, taking 3d12 Fire damage on a failed save, or half as much damage on a success.

The flames scorch the surface, causing it to burn until the end of your next turn. Any creature that enters the area for the first time on a turn or ends its turn there takes 1d6 Fire damage.

At Higher Levels. The initial damage increases by 1d12 and the secondary damage increases by 1d6 for each slot level above 3. The length of the Line increases by 30 feet for every two slot levels above 3.