The Interloper series is an ongoing mystery alright, but the REAL ARG began on October 25, 2022 when Anomidae uploaded 'INTERLOPER: Half-Life 2's Greatest Unsolved Mystery' onto YouTube. It was SO well done, lots of people actually believed it, right up until they reached spoiler territory where I am unable to say anymore. I can assure you it is still an enjoyable expirience. Especially given the fact that you can actually interact with the custom video game levels made for this ARG to discover intresting secrests and other ways on how the Source game engine works. Now you may not need Half-Life 2, but you will need at least one game made on the Source game engine. I am very happy to say this ARG goes beyond Half-Life.