Venfiels' Fireball

A lightless black void like beam shoots from the focus point of a casters power towards their target. Upon striking their desired location black smoke emerges from the contact point like a trickling faucet in reverse before swiftly coalescing into a Dome of Voidlike Black Flame that engulfs their target and anything near it in a 100 ft radius. This spell emits no force upon detonation, but instead expands out to roughly 100 ft like the shade of a cloud passing over a field.

This spell does 20d8 Fire Damage + 5d6 Necrotic Damage to all targets within the spells radius.

 Anything caught within the radius of this manifestation of death must make a Con save or take full damage. Half as much on a successful save. 

If a target hits 0 hit-points because of this spell then they will need to make all three death saves at once. If they pass two saves then they will stabilize but their Constitution will be reduced by 1d4 permanently, or until Greater Restoration is cast upon them.