Riven is not a killing character, because she is not a assasin, she is actually a assistance fighter. the damage that she will make is base on the frozen mallet,atma´s impaler and bloodthirster. Riven will be an off-tank switching bloodthirster for thornmail that will depends on the enemy team, if the enemy team have more physical damage is better to use thornmail, if the enemy team have more magical damage is better to use force of nature or guardian angel.