This achievement is gained with natural story progression so don't worry about missing it.
You'll unlock this achievement upon completing act 5, you'll enter the FLDSMDFR and progress to the last portion of the game, don't worry if you still need to mop up a few achievement though because once you've completed the game you're able to go back and play any level you want.
If you're stuck on a particular part of the game and need to know what do, look here;
http://bit.ly/e5ULzK, where threetimes has made an excellent guide.