Azareck's Chaos Flame

You summon a prismatic, chaotic flame of Abyssal power that burns everlasting and fiercely. These flames are completely inextinguishable under normal circumstances .

Creatures of your choice that are caught in the cylinder must make a Dexterity saving throw, and on a fail taking 10d8 fire damage that ignores resistance and immunity to fire damage and be cursed with the chaos flame. on a pass they take half damage and they aren't cursed.  The caster can use a bonus action to dispel the flame and curse.  

 The curse can be cured by a Greater Restoration, Heal or Wish.

At the beginning of each of an effected creatures turn they take 1d6 fire damage. These flames effect only the target. Furthermore they have disadvantage on a save of your choice and whenever they take damage they take a further 1d6 fire damage 

The original flame can only be dispelled via a Wish spell or if the caster wills it.

At Higher Levels: When you cast this spell with a spell slot of 8th level or higher, the initial damage increases by 2d8 and the curse damage increases by 1d6.