Brittle Keys are generally obtained as event map area completion rewards and Witch Gate completion rewards. Brittle Keys can only be used during the event period. This also applies to Brittle Keys in Presents; while they are listed in Presents for the full 90 days, they will immediately disappear from your Items if you wait until after the event period ends to receive them. Sturdy Keys are available for purchase from the Shop and can be used at any time. When entering the Elemental Hall, Brittle Keys will always be used first. Some of the benefits of entering an Elemental Hall include: