The Sword Essence is one of the Team Instances you can go to. You can either invite people to be on the team with you or you can let the system find a team for you. There's a chance that you can win Baal's Boots, Rolling Rune, and a Soul Chest. On the hard mode you can win Baal's Boots, Rolling Rune, and Warrior Certificates. The boss of the Sword Esscence is the Black Blade Shadow.
Advertisement