So one day, when I had that kind of gamer-ADD where you start jumping around on everything, I noticed that you can jump up to the clifftops on Nightfall very easily. Once you do that, you can force the map to not load any enemies. If you continue onwards and forklift-glitch yourself to the end, the ending cutscene won't trigger and you can explore that small area. Here is how you do it: Nightfall Glitch: bypassing the ending cutscene - YouTube
Nah, I discovered the glitch like a month ago and just didn't have the time to do it until today. Doing the campaign challenge did motivate me to finally make the video, though.
I'm assuming that you can't complete that daily challenge where you have to beat a campaign mission in under 12 minutes whilst doing this, can you.