This is not a complete guide, but some advice for some achievement breaking/run ending game bugs. I did this achievement with two controllers in local, with one on casual (inviting a buddy in for the bike and the last boss). Perf3ct Chaoz has written a great breakdown of section by section, but please read the below before starting the run.
So to just add to the above solutions, there are two known potentially broken checkpoints that can end your iron man run, even if you are exploiting the cloud saves. I hit these two checkpoints on two separate runs, finally getting the achievement on my third attempt, so know first hand how frustrating this can be.
I wanted to add these notes (whilst not a complete solution) to help people avoid having to do multiple runs. As you can see from my link on the official forums (https://gearsofwar.com/en-us/forums/e9b54fc61eb74ad783d533ca...
) as well as posts on the TA forums, this is quite a common problem.
These are the two specific areas and how to avoid backing up a broken game save.Act 3 Chapter 3 : At the Doorstep"There is a buzzkill next to some scaffolding. Its right before you fight some swarm drones. Close the nests when you can. These drones carry lancers (so be careful not to get chainsawed). When you shoot the bridge down 2 snipers and a gnasher drone will spawn on the other side of it."
(Credit to Perf3ct Chaoz for this description)
At the point you close the nests, and before
you shoot down the orange bridge supports there should be a checkpoint. DO NOT back up or shut down your xbox after this point until you have finished the chapter. There is a bug that can stop the first wave of enemies in the next area spawning, meaning you will be unable to cut through the slime and progress.Act 3 Chapter 6 : OriginsAfter the section where there are two snipers, up on the walk way and a scion bursts through the door, you'll come to the loader. As you progress through this section there will be a mulcher stood on top of some yellow crystals. Once you knock him over the edge you'll break the loader and go through a door way. Here you will get a check point. BACK UP at this point, as the next checkpoint, in the room with the snatcher itself is the second glitched checkpoint
If you die in either of the specific areas where the bugs can be found, load up your save from the two earlier points I mention above, as running into the area again should fix the glitch.
I believe these to be the only bugged checkpoints, but if there are any more please let me know and I can add them.