Black-Flame Blade

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and is seared along the wound with a strange, unnatural fire. The target takes 1d6 fire damage, and the first source of healing the target recieves before the end of its next turn is reduced by half (rounding down)

At Higher Levels. At 5th level, the melee attack deals an extra 1d6 fire damage to the target on a hit. The damage of both rolls increases by 1d6 at 11th level (2d6 and 3d6) and 17th level (3d6 and 4d6).