You select setting when starting a new game. After that, it can be altered at any time in the options menu.
Easy: This difficulty is suitable for players inexperienced with action games or the Arkham game series. Enemy health, damage output, reaction time, hit accuracy, and movement speed are all at their lowest settings.
Normal: Arkham Knight’s standard difficulty. Enemy parameters escalate chapter by chapter. As the story progresses, foes become slightly quicker, smarter, and more powerful. On normal difficulty only, this adjustment is dynamic. If you perform gracefully, dispatching combat scenarios with freeflow ease and stalking predator scenarios unseen, difficulty increases slightly. However, if you take many hits in combat or get seen often when sneaking around then the game becomes slightly easier.
Hard: This is the setting for experienced Dark Knights. If you’ve cleaned out the other Arkham games and chewed up and spat out their challenge rooms, this is probably the setting for you. On Hard difficulty, enemies in a given level behave as they would five chapters later on Normal. For example, in Hard difficulty’s chapter 3, enemies act like they do in Normal difficulty’s chapter 8. The difficulty won’t subtly adjust based on your performance, either. You’re stuck at five chapters harder no matter what, though if this ends up being tougher than you’d like, you can change it back to Normal or Easy. Arkham Knight doesn’t have Achivements or Trophies based on difficulty, and WayneTech Upgrade Points earned are the same too, so you’re free to pick the difficulty setting that is most fun and rewarding for you.