Talk:Nightmare Mode/@comment-8610408-20130714143211/@comment-71.254.124.61-20130715033212

I think you're misreading it. It's not saying you are guarenteed to get a different reward each time you run the mission. It's saying the reward is not set in stone before you even begin like alert mission mystery prizes are, and if you ran the same mission 100 times you'd be unlikely to get 100 of the exact same mod.