Originally Posted by Joseph0714
Let us know if Ultra Nightmare works that way :P
It doesn't. Just beat the DLC and the achievement for Ultra Nightmare didn't pop. I have one last thing to try though. For some reason my game has the final mission as not completed even though I completed it months ago. I'm going to try and run through that mission as a last ditch effort before starting the game over.
Edit: Didn't work. Gonna have to play through the game again.