The Costume Chamber is a special Summon Gate that can be used to summon a Classic Hero and their Costume. The Costume Chamber can only be accessed when The Masquerade event is ongoing.
Costume Summons can be made with Costume Keys or Gems. Costume Keys can be obtained through completing stages in The Masquerade. They may also be awarded as loot in certain parts of the game (Mystic Vision, War Chests, Wanted Missions).
Each Costume Chamber comes with two Featured Legendary Costumes that have an increased chance of being summoned. You can always check the exact probabilities by tapping the blue circle icon with an "(i)" in the top left corner.
The Masquerade is held at 07:00 UTC every eighth Thursday and lasts for 48 hours; precise schedule information can be found in the official monthly event calendars we publish on our Community Forum. Please note that you must be Level 18 or higher to access this event from the Quests Map.