When you attune to the Thieves Crown, you add 2 to your dexterity.

Once per day the wearer of the crown can decide to increase the dexterity bonus to +6 for a minute. This increase can exceed the normal 20 ability score maximum. When this ability is used the original 2 dexterity increase is nullified until after the wearer finishes a long rest.

Notes: Bonus: Dexterity Score, Bonus: Dexterity Score