Entropic Athame

A pale, curved dagger of bone appears in your hand, oozing black ichor before racing off towards its victim. Make a ranged spell attack against a creature you can see within range, dealing 3d4 necrotic damage on a hit. 

A creature that takes damage from this spell must make a Constitution saving throw at the beginning of their next turn. On a failed saving throw, the creature takes additional necrotic damage equal to twice the damage rolled, while on a successful save they merely take additional necrotic damage equal to the amount rolled. 

While not among them, this spell does trace its origins back to the 96 Sealed Enochian Runes, as evidenced by its unusual and deadly nature.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, on a failed saving throw, you multiply the spell's damage by 1 + the spell's level, while on a successful save the damage is merely multiplied by half the spell's level (round up).