Boon of Combat Prowess

 When you miss with a melee weapon attack, you can choose to hit instead. You can use this boon threes times afterwards you can't use it again until you finish a short rest.

An Epic Boon is a special power available only to 20th level characters. Characters at that level gain such boons only if the DM wants them to and only when they find it appropriate. Epic Boons are best awarded after the characters complete a major quest, or accomplish something else particularly notable. A character might gain an epic boon after destroying an evil artifact, defeating an ancient dragon, or halting an incursion from the Outer Planes.

The text of a boon addresses its user. Unless a boon says otherwise, a character can't gain it more than once.