Beshaba's Curse

A streak of roiling necrotic energy flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of purple and black flame. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 10d6 fire damage on a failed save, or half as much damage on a successful one.

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

If this spell makes direct contact with a creature, the spell's second effect begins. A small piece of the goddess Beshaba is deposited inside the creature's body and it begins to take hold. The creature must make a Constitution saving throw (DC25) immediately and every round afterwards. On a successful save, the creature is able to resist Beshaba for that round but they cannot take an action. On a failed save, the creature takes 10d10 Necrotic damage. If the creature drops to zero hit points while under the effects of this spell, their body is ripped apart by pure Necrotic energy and Beshaba can take hold of their soul.

The only way to remove Beshaba's Curse is by casting a 9th level Dispel Evil and Good on the creature before they succumb to the effects of the spell.