Dafar: When you make an attack roll, if the defender is your rival, you may re-roll one die of the roll. When you make a basic attack, if the defender is not your rival, the attack deals -1 damage, to a minimum of 1.
"Ere shadows were, ere night was gone,
I found the one whom suns had sought."
-Clark Ashton, "Echoes of Memnon"