Death Throes

You flood a target creature's body with necrotic energy, causing an explosion of pain.  The target makes a Constitution saving throw, taking 8d10 necrotic damage on a failure and half as much on a success.  If the creature has half or fewer of its total hit points remaining when you cast the spell, it makes its saving throw at disadvantage.  If the target is killed by the damage dealt to it by this spell, the necrotic energy overflows and each creature within 20 feet of the original target must also make a Constitution saving throw, taking 4d10 necrotic damage on a failure and half as much on a success.

At Higher Levels:  When cast using a 6th-level spell slot or higher, the damage to the original target and to nearby creatures increases by 1d10 per slot level above 5th.