Modders have managed to restore or discover cut content in From Software’s Dark Souls series (and spiritual successors) for a while now. And now, you can add the ability to add custom maps, as well. Modder Dropoff has managed to import Half-Life‘s deathmatch map Crossfire into the original Dark Souls.

According to this Reddit thread, a user known as Katalash explains just how difficult it is to actually pull this off.

“The main roadblock for custom maps in Dark Souls is that all the Souls games use Havok for physics and collision detection, and all the games’ collision data is stored in a proprietary Havok format, and From added their own customizations on top of the format,” Katalash explains.

“To further complicate matters, the file format and stored data change drastically between game to game. The collision for this was made using an old version of Havok Content tools that was released publicly for a short amount of time before Havok stopped distributing new versions of the tools. The tool generates collision compatible with Dark Souls: Prepare to Die Edition, and Dark Souls 2, but won’t work with Dark Souls Remastered or Dark Souls 3 and beyond.”

Modders Meowmaritus and Horkrux worked to create the tools to import models and collision, respectively, but don’t expect this to be the start of modders being able to add new maps and overhauls just yet, however. Katalash points out that the map doesn’t feature enemies or NPCs at the moment because they require custom navigation mesh data, which the community unfortunately doesn’t currently have the ability to make. The search for the next piece of this puzzle continues.