This isn’t too hard of an achievement, especially on Easy difficulty.
First, when you start up a new game, select Easy difficulty.
Next, you’ll need to go through the entire storyline campaign from start to finish. Here’s some tips to help you.
-Make sure you take the time to find collectibles, like the Riddler trophies and tapes. They will help you upgrade Batman faster, allowing you to have an easier time with predator and combat situations.
-For combat, always make sure to deal with guys that have weapons in their hand. If they are too far away, use a Batarang to knock them out. Big guys will always be a threat, like the Titans, so deal with them first, then work on the small fry like normal.
-For predator, don’t do anything fancy. Make sure the bad guys are separated from each other, then use silent takedowns. If they spot you, quickly fly up to a gargoyle and move onto different ones until you lose their line of sight.
-Bosses are different in each case. Take your time with them. If you die, no problem, just restart the boss fight and try again.
Once you defeat Joker in his final form, the game will end and the achievement will unlock as the last cinematic scenes play out.
Have fun and good luck!