Fortunate

You are favored by a font of fortune. 

You have 1 fortune die, which is a d20. A fortune die is expended when you use it. Whenever you make an attack roll, an ability check, or a saving throw, you can roll your fortune die. You can choose to roll your fortune die after the initial die are rolled, but before the outcome is determined. You choose which of the d20s is used for the attack roll, ability check, or saving throw.

You regain your expended fortune die when you finish a long rest, or when you critically succeed on an attack roll or death saving throw.