If you want to play the Adventure-Horror-Game Downfall on Linux, you’ll currently also need The Cat Lady, because it needs some libraries from this game to start. Tested on Debian Jessie 64bit:

1. Install Downfall and The Cat Lady via Steam
2. Open the the data-dir of both install-folders, eg. /your/path/SteamLibrary/steamapps/common/Downfall/data and /your/path/SteamLibrary/steamapps/common/TheCatLady/data in your favorite filebrowser
3. rename the libs32 and libs64-directories of Downfall to eg. libs32.old and libs64.old
4. copy over the complete libs32 and libs64-folders from The Cat Lady to Downfall
5. if you want to double scale the screen-size, open the file /your/path/steamapps/common/Downfall/Downfall in a text-editor and append "–gfxfilter hq2x" on the execution line, like: … “$SCRIPTPATH/data/ags64” “$@” “$SCRIPTPATH/data/” –gfxfilter hq2x There are 2 lines like that, depending if you run the game in 32 or 64 bits. Source: Steam Forum