Okay now I understand how they’re pulling this off and it’s pretty cheeky. They’re just running two game instances and hijacking the game’s pipelines to brute force cross-interaction between them. It’s a really clever shortcut approach, but it doesn’t run like a traditional mod where you only have one game running and the content is embedded in the mod itself running under the game’s pipeline and engine toolset. To explain it more thoroughly, say you have two games: Game A and Game B, and some agent program between them. Game A provides some approximation of its state to Game B in a format that it can decode into its own state. Game B plays off of this state, then sends its state back in a way that Game A can decode into its rendering pipeline, physics, gameplay, etc. The agent cannot render or simulate Game B in Game A unless both games are running.