Umbra Blade

You wreath your blade in shadow energy and strike at your foe, seeking to poison its shadow with your malice.

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails.

On a hit, the target suffers the attack's normal effects, and its shadow begins to circle around it menacingly until the start of your next turn. If the target willingly moves before then, it immediately takes 1d8 necrotic damage, and the spell ends. 

At 5th level, the melee attack deals an extra 1d8 necrotic damage to the target, and the damage the target takes for moving increases to 2d8. Both damage rolls increase by 1d8 at 11th level and 17th level.