If the patch fails entirely, you can try a method: Use steam_api.dll from a known working game (e.g., Rivals of Aether community build) and place it alongside the patched .mfx .
Understanding the Steamworks.mfx Error and How to Fix It If you have encountered the error message you are likely trying to launch a game built with the Clickteam Fusion 2.5 engine. This specific file acts as an extension that bridges the game engine with the Steam API. When it is missing, corrupted, or "unpatched," the game will fail to start. What is Steamworks.mfx? steamworksmfx patched