An unofficial patcher to get Batman: Arkham City GOTY Edition to execute as the non-GOTY version on Steam.
The main purpose of doing so is if you'd like to finish some achievements on the non-GOTY version, but are unable to launch it any more due to being unable to activate it. It works by patching the GOTY version's executable to use the non-GOTY version's App ID (and patches out code that verifies the executable). After patching, you MUST launch the game through the .exe directly, as launching through Steam will force it to use the GOTY version's App ID, and then the game will try to re-launch the non-GOTY version since it sees mismatching IDs between the executable and what's running.