Unicorn Firebolt

You summon numerous tiny unicorns made of fire to attack the target within range that you can see. Make a ranged spell attack against the target. On a hit, the target takes 1d8 fire damage. On a critical hit, the target is also knocked prone by the tiny unicorns who jump all over the target and then disappear.   

This spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).