Moonlight

Moonlight is a possibly-guaranteed artifact sword. On top of being a fantastic weapon, the sword is the subject of a quest with Lord Ghazkhar, who will pay you one gold for its return.

While the sword is very heavy (a high attack speed is required to use it remotely well), it boasts some very desirable magical effects including Magic on Miss, Corrosion-proof, Indestructible, and 25% extra experience. The Indestructible attribute is particularly useful as it allows the character to utilize the power tactics without fear of destroying their weapon. This greatly increases the damage output the sword, as its attack damage is on the lower end of artifact weapons.

As of now, the only known way to find the sword is to complete the Razi quest involving killing the Slavers. The weapon is one of the random rewards generated from the completion of that quest.