The feathers were alright, the only problem was that after I finished the guide I actually missed one feather and had no idea which one it was, so I had to run from the beginning again.. Luckily it was halfway through the guide so it wasn't so bad.
- Start up your file with your gamertag logged in on player 1.
- Connect a second controller, but don't log in any gamertags.
- Press Start on the second controller.
- Go into the simulator, and redo every big boss battle. From Tinkerer all the way to Nick Fury. Basically every boss that counts towards the achievement.
- If you don't have a second person to help you, press Select on the second controller to switch it to AI during battle. You'll have to keep pressing it after every cutscene though.
There's a list somewhere around the MUA2 sub-forum. Congrats on the Crab achievement btw.