You can use a bonus action to speak this magic sword's command word, causing black flames to erupt from the blade. These flames shed dim light in a 40-foot radius. While the sword is ablaze, it deals an extra 1d6 fire damage and 1d6 necrotic damage to any target it hits. When this happens, the DM chooses one creature other than you within 30 feet of the target (preferably one of your allies). The black flames leap to that creature, causing it to take half of the fire and necrotic damage.

The black flames last until you use a bonus action to speak the command word again or until you drop or sheathe the sword.

Curse. The weapon is cursed, a fact that is revealed only when you attune to it. The identify spell is deceived by the curse and falsely reveals the item to be a flame tongue greatsword. Attuning to the weapon curses you until you are targeted by the remove curse spell or similar magic. While cursed, you refuse to wield any other weapon, and you refuse to attack with this weapon without activating its flames. You have disadvantage on attack rolls using the weapon against fiends. Also, if a creature that is missing hit points leaves your reach while you are wielding the weapon and its flames are active, you must succeed on a DC 20 Wisdom saving throw or else be forced to use your reaction to make an opportunity attack against that creature if you are able, even if the creature is your ally.

Proficiency with a Greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Damage: Fire, Damage: Necrotic, Disadvantage: Melee Attacks, Damage, Combat, Cursed, Heavy, Two-Handed, Graze