Aspect of Pain, Duriel's Darkrider, is a unique Armaddon found in Silver Spire Level 1 in Diablo III. In Adventure Mode, it can be encountered in Gardens of Hope, second tier.
In Campaign, it is initially disguised as Zoltun Kulle's ghost, attacking when spoken to. One may skip this fight at will, though.
In combat, it has Extra Health and Frozen affixes.