Devouring Inferno

You focus your very being into your palms as you let out an infernal yell as you let out a twisting, whirling 30 foot cone of blue fire as those hit would feel that their very soul is wretched from their bodies and burned away.

When in range of the spell you must make a Dexterity saving throw or take 6d10+10 fire damage plus 4d8 force damage. On a fail they take full damage and are thrown 15 backward. On a successful save the victim takes half damage and is not thrown backward. 

If a victim is killed with the spell the entity must make a Death saving throw of be instantly incinerated into ash and only extremely powerful magics (I.e. an True Resurrection or wish spell) can revive this entity.