Devil’s mark

A veil of darkness fall on a group of enemies, each foe hit has to make a Wisdom 14 save, if they fail they take the full effect, if they succeed they are unaffected. Affected enemies take 2d6 damage every time it becomes their turn for as long as they are in the area. 

at higher levels, the spell’s damage increases by 1d6  and area of effect increases by 10ft each spell level.