Start by playing through the main story on normal difficulty and completing all the side missions. There are 21 bronze trophies available just for story-related tasks.
With the main story finished, you’ll need to focus on the 243 Riddler Trophies (a form of collectible within the game) and completing Riddler’s side missions that start when you collect a certain amount of these. At the end of that you will get the Riddle Me That trophy.
You should now be at 100% completion on the main game, which will allow you to trigger the Knightfall Protocol – the game’s true ending – and earn the Knightfall trophy.
The next phase will be the AR challenges – these are short combat, stealth, or Batmobile challenges that have a star rating for your performance. These unlock as you progress through the main story, so all 23 main challenges will be available now.
You need 69 stars for the trophy, which is 3 stars on all these 23. But, additional challenges from DLC will count towards your 69 total, which will make this part very easy if you have DLC available.
You can use the AR challenges to clean up any miscellaneous combat related trophies that you didn’t get in your main playthrough. This may also include Brutality 101, the trophy that most people have the most problems with, but don’t spend too much time here as there’s a perfect opportunity for this coming up next…
So, you should now only have The Long Halloween trophy left, and maybe Brutality 101. It’s time to do it all again in New Game + to earn The Long Halloween. This is standard New Game + rules – you start with all your equipment and upgrades from your first playthrough, you can ignore side missions and collectibles and just focus on the main story. Enemies hit harder and you won’t get the prompt to counter when an enemy is about to hit you, so you’ll need to rely on the animations.
If you’re still in need of Brutality 101, then try to get it during New Game + during the Joker fight on the bridge towards the end of the game. The Joker has no health here and it’s impossible to defeat him unless you do the button combination to put him in the box at the end. So you can wail on him and use the pick up move when he goes down to keep your combo going and unleash all the required moves.
And that’s it. A solid platinum to add to your collection.