Curse of Planar Flames

You curse a target creature that you can see within range, wreathing it is ghostly blue, green or violet flames. The target immediately takes 8d10 + 20 fire damage as the spectral flames engulf its body. 

At the beginning of each of its turns, the cursed target makes a Charisma saving throw. On a failed save, the target immediately suffers an additional 2d10 fire damage as it continues to burn. If the target succeeds on the saving throw, the flames are momentarily calmed. If the target succeeds on three saving throws, the curse immediately ends. These successes do not need to be consecutive, but if it fails three saves in a row, it loses all recorded successes and must start again.

In addition to harming the target, the curse prevents the creature from becoming invisible. The flames shed dim light in a 10 ft. radius, and do not burn anything other than the cursed creature. The flames cannot be extinguished by water or other non-magical means, and are immediately extinguished when the target dies or if you choose to end the spell using an action. If a creature dies while cursed in this way, its soul is destroyed, and it cannot be restored to life or become an undead of any description by any means short of a wish spell. 

When you cast this spell as a ritual, the range of the spell becomes 300 feet, and you do not need to be within line of sight with the target. However, the spell requires 200 gp worth of expensive inks with which to draw a planar sigil on a flat surface, and which the spell consumes.