Source: Tal'Dorei Campaign Setting Reborn

Weapon (greatsword), legendary (requires attunement)

This blade appears to be a beautiful cruciform sword of shining silver, inlaid with sparkling rubies. You gain a +3 bonus to attack and damage rolls made with this magic weapon, which has the following properties.

Corrosive Submission. When you hit a creature that has an Intelligence score of 4 or higher with an attack using this sword, the target takes an extra 3d6 acid damage and must succeed on a DC 17 Charisma saving throw or be charmed by you for 1 hour. If you attack the creature again while it is charmed in this way, the extra acid damage increases to 10d6 and the charmed condition ends. If the target succeeds on its saving throw or the charm ends for it, it can’t be charmed again in this way for 24 hours.

Hidden Nature. The acid damage dealt by this greatsword appears to be radiant damage to all who perceive it. A True Seeing spell or similar magic reveals that the sword is actually a rusted, pitted blade dripping with acid.

Sentience. Graz’tchar is a sentient neutral evil weapon with an Intelligence of 14, a Wisdom of 12, and a Charisma of 18. It has hearing and darkvision out to a range of 120 feet.

The sword can speak, read, and understand Common, and can communicate with its wielder telepathically. Anyone who holds it hears the wise voice of a sorrowful king, beckoning the user to seize their destiny. A creature that succeeds on a DC 26 Wisdom (Insight) check while listening to the blade’s voice hears a sliver of malice that suggests the truth: the voice is a corrupting trick of the Demon Prince of Indulgence.

Personality. Graz’tchar slowly attempts to sway its wielder to sow chaos in Exandria, telling lies and spreading malign truths about great leaders, and claiming that the members of the Tal’Dorei Council are corrupt and must be overthrown. The voice of this blade is actually the Demon Prince of Indulgence, speaking from his Abyssal prison.

If the sword’s attuned wielder disobeys the urges of the weapon for an extended period of time, Graz’tchar can attempt to control the wielder, who must succeed on a DC 17 Charisma saving throw or become charmed by the sword for 24 hours. While the wielder is charmed in this way, the sword can compel them to take an action of the sword’s choice once per hour, though the wielder believes this action is taken of their own free will. If the chosen action leads to the harm of someone the wielder considers a trusted friend or ally, the charmed condition immediately ends. On a successful saving throw or if the charmed condition ends for the wielder, they are immune to this property of the sword for 24 hours.