Bone Volley

The user conjures a black cloud with souls flying in and out wailing in pain and horror. On the user's mark, arrows made from the bones of those killed by the user rain down and pierce anything in a 15x15 ft box. Anything in the box must make a dex saving throw opposed by the user's ranged attack. On a failed saving throw, the spell does 3d12 necrotic damage+1d4 for every enemy killed during this combat and is must make a strength saving throw opposed by users original attack roll or be pinned, this process repeats every turn. On a succeeded saving throw the target takes half the damage and is not pinned. 

Add 1d12 dmg to attack for every level cast above 3rd.