You release withering energy in a 15 foot cone. All creatures in the area must make a constitution saving throw. On a failed save, a creature takes 3d4 necrotic damage and becomes vulnerable to necrotic damage until the end of your next turn. If a creature is resistant or immune to necrotic damage it has advantage on its saving throw. On a successful saving throw, a creature takes half damage and isn't affected by the necrotic damage vulnerability. The necrotic damage vulnerability does not increase the damage of this spell when you cast it.  

At Higher Levels. If this spell is cast using a spell slot of 2nd level or higher, the damage of this spell increases by 1d4 for every slot level above 1st.