nightmare

[spiral sail]

I joined my friend after he started playing on nightmare and we both finished the story together but neither of us got the achievement for the nightmare difficulty?

[wintry sparrow]

If you change the difficulty at ANY point in a Nightmare playthrough, you get no achievement

So your friend probably changed it

[spiral sail]

damn ight

[spiral sail]

doesn’t matter if it wasn’t my game right? like I should still unlock it if we were to start it over as long as we stay on nightmare?

[wintry sparrow]

I'm not sure

You get the same rewards on co-op though