This massive greatsword is made of carved, jagged obsidian. A dark mist seeps out of cracks in the blade, radiating with the power of the soul held within in the large onyx gemstone embedded in its hilt. The hilt is made of steel and is decorated with intricate runes.

You gain a +3 bonus to attack and damage rolls made with this magic weapon. It has the following additional properties.

Imprisoned Soul. This sword was forged by giants in order capture the soul of the dracolich Zynnyth, the Black Flame, and even then, it was not fully able to seal his power. This greatsword has the reach property and deals an extra 2d6 fire damage to any target it hits. This increases to 3d6 if the target is of good alignment.

Black Flame's Will. This sword will stop at nothing to eliminate any who stands between it and its liberation. This weapon gains a number of charges equal to your proficiency bonus, rounded down. When you miss with an attack, you can choose to spend a charge to cause the weapon's flames to leap from the blade to the attack's intended target. The target takes 2d6 fire damage, or 3d6 if they are of good alignment. The weapon regains all expended charges after a long rest.

Draconic Fortitude.  The powerful bond with the dracolich has strengthened your mind and your will. While attuned to this weapon, you have advantage on Wisdom saving throws and Wisdom (Perception) and Wisdom (Insight) checks. You also cannot be charmed or frightened.

Frightful Presence. On your turn, each creature of Zynnyth's Rest's choice within 30 feet of you and aware of you and the sword must succeed on a DC 21 Wisdom saving throw or be frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the sword's Frightful Presence for the next 24 hours. The sword decides when to use this ability.

Sentience. Zynnyth's Rest is a sentient lawful evil weapon, named for the soul of the ancient dracolich imprisoned inside it, with an Intelligence of 18, a Wisdom of 15, and a Charisma of 30. It has hearing and darkvision out to a range of 120 feet and blindsight out to a range of 60 feet.

The weapon can speak, read, and understand Common and Draconic, and can communicate with its wielder telepathically. Its voice is deep, grating, and echoing. 

Personality. Zynnyth is an ancient shadow dracolich native to Shadowfell. He despises all life, but he especially loathes the giants for imprisoning him inside the sword.

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

Notes: creature of non-good alignment, Heavy, Two-Handed, Graze