As mentioned in the other solution, playing on "hard" will unlock the other difficult-related achievements as well. Therefore, it is strongly recommended to play the game on this difficulty, since it is not hard at all. The fights are straight forward and most of the boss fights are easy, too.
Some tips I want to give you for your hard playthrough:
1. As you go through the game, collect as many collectibles as you can get. You'll get lots of XP and you will be able to upgrade faster.
2. When you upgrade Batman, focus on the combos and health upgrades first. Both will make fights a lot easier. Being able to us combos like
after a x5 combo will make the bigger fights easier. Health upgrades are especially useful in the latter boss fights. Don't wait to long to upgrade those. Personally, I found the gadgets upgrades to be negligable. They are more useful in the challenges, but that's just my way of playing the game.
3. The biggest challenge will be the boss fights. Every boss has a snag to himself. As soon as you found his weakspot, the fight will be relatively easy. I provided links to video guides in all the respective achievement solutions. If you get stuck in one particular fight, refer to the strategy mentioned in those videos.
Last but not least, I' ll provide a link to a playlist with videos of a full 100% hard walkthrough of the story down below. https://www.youtube.com/playlist?list=PLUae2dewdNcwyW7UsYfkM...
(videos by: tuus4)
Hope this helps you guys!
Any improvements? Please let me know in the comments below