You can change your reward at random into another one. The more often you re-roll, the higher your chance to get a better reward. You cannot change back after re-rolling, however, so choose wisely.
Upon opening you have a choice to take the item displayed, or pay Yang to change the reward. The more times you change, the higher the cost, up to 15 times. In fact, the cost doubles each time you want to change the reward.
