Reach level 11.
The Emerald Mystery mini-event will temporarily give you access to the special Sealed Chest that contains lots of valuable prizes, including several unique rewards. 

Find a Candle of Clarity, an item that gives you access to a special game mode where collecting items highlighted in green will get you emerald fragments required to open the Sealed Chest. A Candle of Clarity is active for 15 minutes and is stored as a single item only.

Please note that you can only play the special mode by pressing the Play button in the Emerald Mystery mini-event window!

If you collect the required number of emerald fragments, you will be able to open the chest and get 3 random items from the chest's contents. Don't worry if unique rewards don't drop the first time you open it. Each time you open the Sealed Chest, it increases your chances of getting unique rewards! However, if you receive a unique reward, your chances are reset.
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