You will have to complete a little fetch quest to gain entry to the Emberworks. Specifically, you will be on the hunt for a crown located in the Forgotten Halls. You will have to cross the Sundered Battlefield once again in order to find the Halls. Use this as an opportunity to grab anything that you may have missed during your first trip through the massive Sundered Battlefield area. Enter the Halls when you find them.

This area is full of undead enemies. Sounds simple, but these guys have a few tricks up their sleeves. The enemies here are tough, and can take quite the beating. They are also resistant to Interruption, making them tough to avoid when they start hitting you. Slow them down and ping them from a distance with ranged attacks when you can.

Follow the waypoint marker to the boss of the stage, Thiss. This gnarly undead dragon boss has tons of health, just like his minions but proportionately stronger. His acid breath attack can wear away your health with surprising quickness. Avoid it whenever possible by rushing off to the side when you see him winding up to spew his nasty breath your way. During this fight, keep a careful eye on your health bar and use potions liberally. Just like every other boss, Thiss will summon minions at some point during the battle. As usual, peel away from the main fight and take your time eliminating all of the new threats. When the lesser enemies are gone, you will have a clear path to Thiss.

Return to the fight, and keep doing what you've been doing. Wear his health down slowly but surely. As the battle weasrs on, you may find that it's best to keep to Thiss' flanks. That means sticking to either the right or left side of the boss, where it will be harder for him to target you with his acid breath attack.

When the boss falls, grab the crown from him and return to the Emberworks to turn it in.