Burning Embers

A beam of burning embers streaks toward a creature within range. Make a ranged spell attack against the target. On a hit, it takes 1d8 fire damage. Until the start of your next turn its speed is reduced by 10 feet as the fiery embers spin round its legs in a vortex. 

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