Delvar's Black Flames

You conjure a faint purple spark in the palm of your hand, and the spark bursts into a fiendish black flame, which erupts into a baleful inferno. These flames do not feed on the air as normal fire does. Instead, the flames consume the life force of any creature unfortunate enough to make contact with it. As a result, no physical harm will come to anything affected by the flames. The dark flames you have summoned are otherworldly, and cannot be extinguished by normal means, except by the flame’s creator, or a number of specific conditions.

Each creature within a 60 ft. cone must make a Dexterity Saving Throw. On a failed saving throw, the creature takes 8d10 Necrotic damage and is set on fire. The creature will continue to take an additional 1d10 Necrotic damage at the beginning of their turn, until the caster dispels the flames, the target dies, or a Greater Restoration spell is cast on them. On a successful save, takes half damage and is not set on fire.

Constructs, or otherwise soulless creatures (DM's discretion) are unaffected by the flames.