Fortune seems to smile on you in many ways. When you complete a long rest, roll two ten-sided dice, and set them aside.
When you make any attack roll, defence roll or saving throw, you may substitute either of the ten-sided dice rolled with one of your reserved dice. This expends the reserved die.
When a foe makes an attack roll against you, and that attack includes no other creatures among its targets, you may substitute either of their ten-sided dice with one of your reserved dice. Again, this expends the reserved die.