Open BmGame\Config\BmEngine.ini and add these lines under [Engine.ISVHacks] :
Suddenly, your game feels like it's swimming in molasses. The framerate tanks to 15 FPS. You think your PC is too weak? Unlikely. This game is from 2009. batman arkham asylum x ray room lag repack
Fix for Batman: Arkham Asylum X-Ray Room Lag in Repack Versions Open BmGame\Config\BmEngine
This forces the game to load the entire X-Ray room into RAM at once, bypassing the streaming decompression lag. You will see a 2-second freeze when you first open the door, but thereafter, the fight will be smooth. the fight will be smooth.