To detect if the Steam version of the game is a pirated copy, the game registers a fake DLC ID with SteamAPI. If a Steam emulator unlocks all DLC, the game won't progress past the first chapter and will open browser windows to the Steam page of the game every frame, potentially freezing your computer for having too many tabs on your browser.

pack/database/stat.rbrb also contains this text about a popular Steam emulator. It's referenced in the exe so it's not completely unused, but if it actually triggers anything is unknown.

"steam_api.dll.ali123
ALI123.INI
- STEAM NOT DETECTED! RESTART GAME TO ENABLE STEAM FUNC! -"

As of 2.00 the game also checks the integrity of steam_api.dll and will softlock after defeating a boss in Chapter 2 by disabling your controls.
Contributed by MehDeletingLater