Coil’s End

You channel your rage into pure necrotic energy with which you you to attempt to snap the targets hold on the mortal planes. The target must make a Constitution saving throw. The target takes 5d12 necrotic damage on a failed save, or half as much damage on a successful one. This spell has no effect on undead or constructs.

If the target is killed this way they may only return to life via a wish spell 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d12 for each slot level above 3rd