Eviscerating Cascade

You reach out with your hand and send a cascade of small sundering explosions directly through insides of the enemy's body. 

Make a melee spell attack dealing 4d6 fire damage on a hit.

Choose a number from 1 to 6. Hit creature must make a Constitution saving throw. A target takes 1d6 fire damage for each instance of a chosen number among the rolled dice of the initial spell damage on a failed save, or half as much damage on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the initial damage increases by 1d6 for each slot level above 2nd.