The "story" of is essentially a cat-and-mouse game between Steam's DRM (Digital Rights Management) and a community of users looking to unlock games they don't technically own. GreenLuma is a well-known Steam "SteamApi" redirector/patcher
To make games or DLC appear in your library, you must manually tell GreenLuma which App IDs to "unlock".
I followed a GreenLuma tutorial to unlock DLCs for a few single-player games on Steam. The step-by-step guide I found was surprisingly detailed—covering everything from downloading the right GreenLuma files to configuring bin files and using appid lists.
This is the story of that mirror.