Throw fire

You throw a small ball of fire at one square within 60 ft. of you. Any creature in that space takes 1d4 fire damage. The fire will spread to flammable things adjacent to it that aren’t being worn or carried and lasts for 1 minute. during this time, any creature who starts, ends, or moves through the fire will take 1d4 fire damage. The fire can be spread 10 ft. In 1 direction using the gust spell.

at level 5 it does 2d4, at level 10 it does 3d4, at level 15 it does 4d4, and at level 20 it does 5d4.