BonePlosion

Dark purple streak of energy envelops the bones enlarging and transmuting them to a single chunk of bone. When pointed at a place within range it shoots forward with a ghostly scream growing in size until it reaches its final location, upon which it implodes with a deafening silence then immediately explodes in a Dark shadowy purple explosion burning everything in a 20-foot-radius with necrotic fiery damage. Each creature within range centred on that point must make a Dexterity saving throw. A target takes 4d6 Necrotic damage and 3d6 Fire damage on a failed save, or half as much damage on a successful one. The Necrotic fire spreads around corners igniting flammable objects in the area that aren't being worn or carried. 

At Higher Levels: When you cast this spell using a spell slot of 4th  level or higher, the damage is increased by 1d6 of one damage type for each slot above 3rd.