ARGs have gained traction recently. They often present themselves as mysterious narratives across different forms of media, without clearly explaining what they are upfront. As a result, viewers end up investigating these stories themselves, which is why so many YouTube videos exist solely to uncover, analyze, and make sense of them. For people like me, this process triggers a strong sense of curiosity that easily grabs my attention and time.
You can take “Petscop” as an example. It’s a game-inspired ARG that creates a fictional PlayStation 1 game and adapts a “Let’s Play” format into a mysterious narrative. The guy who plays Petscop named Paul play the game, and as he progresses, he uncovers more and more unsettling secrets hidden within it.
There are also web series that blur the line between fiction and reality in a different way, such as The Mandela Catalogue. It’s an analogue horror series that tells its story through fictional emergency broadcasts, VHS tapes, and similar formats, presenting a narrative where “alternates” exist alongside humanity.
In these ARGs, creators leave behind puzzles and fragments for the audience to piece together in order to uncover the mystery. It’s also common for ARGs to take familiar concepts or themes and twist them into something entirely different and unsettling.
There are many interesting web series out there, but there is one that disturbed me in a uniquely convincing way and occupied my thoughts for a long time.
That series is Interloper, an ARG based on Half-Life 2 and the Source engine, presented through an investigative narrative from the perspective of a single investigator. It is a recently concluded web series, spanning from 2021 to 2025 with a total of 15 episodes.
In Interloper, two familiar things are twisted at once: Half-Life 2 itself and typical investigative web essay format commonly found on YouTube.
A friendly warningVery minor spoilers of Interloper ARG ahead but I still recommend having a raw experience by yourself
Enter Interloper
Half-Life 2 is one of my favorite games of all time. Back when I was still using a potato laptop, it was probably the most advanced game I could run. The game is built on the Source engine, which also powers many well-known Valve titles such as Garry’s Mod, Counter-Strike, Portal, and Team Fortress 2. These games aren’t particularly demanding, which is why I spent a lot of time playing Source-based games back then.
Interloper feels unusually realistic and believable because of how it uses the Source engine, in a way that left me genuinely disturbed and immersed. If you’re familiar with the engine, you’ll understand that many of the mechanisms used throughout the ARG logically make sense.
The core concept of the ARG centers around an investigation into a supposed mysterious console command called “INTERLOPE,” which the series presents as existing within Half-Life 2. Within the ARG’s narrative, this command is said to generate demo files, including a specific category referred to as “type 5” demos, which become a central point of investigation.
In Source games, demos are typically recordings of player gameplay. However, within the ARG’s narrative, these demos behave very differently, appearing as if the NPCs themselves are conscious, with footage resembling a first-person point of view seen through their eyes.
This is just one example of the kind of mystery Interloper presents. As the series progresses, viewers encounter references to other Source-based games such as Garry’s Mod and Portal, as well as tools like the Hammer editor. These elements escalate the investigation into something broader and more complex, raising more questions with each discovery.
These familiar tools are presented in ways that feel both technical and paranormal at the same time. For instance, when the investigator begins using the Hammer editor, they first explain its basic purpose and features for viewers unfamiliar with it. Later, the same tool is used to reveal something unsettling. That moment is where the twist happens.
Interactivity and Reactivity
Many of the resources produced during the investigation are interactive. They are available for download, and viewers can examine them using existing Source tools. For example, the “type 5” demos shown earlier can be downloaded and replayed inside their respective games.
This interactivity encourages viewers to form their own theories and share them within the community Discord server. Inside the server, you’ll find voice and text channels dedicated to discussing theories based on individual observations and explorations. At times, even the investigator responds directly to theories shared by the community, reinforcing the sense that this is a collective effort.
These community contributions are often featured in later episodes. Sometimes they appear as fictional elements within the narrative, while other times they originate from viewers who are deeply knowledgeable about the engine and the mystery itself.
In fact, there are episodes where community interaction becomes essential. In one instance, viewers are given access to a server and must solve a mystery within it in order for the investigation to progress.
It creates a genuinely unique experience.
By adapting real Source engine concepts into the ARG, Interloper consistently feels borderline real, blurring the line between technical curiosity and something genuinely paranormal. This creates a strong sense of realism, and for both experienced users and newcomers, the mystery serves as a compelling hook.
Furthermore, the ability to download and examine demos using existing in-game tools significantly elevates immersion. Viewers can investigate at their own pace, discuss findings with others, and gradually converge toward shared theories.
When a theory turns out to be correct and the pieces finally click, the experience feels deeply rewarding and keeps viewers curious about what comes next.
This level of hands-on investigation sets Interloper apart from most ARGs, which often limit participation to passive observation. In many web series, viewers can only rewind videos and piece together information from what’s shown on screen.
Interloper’s responsiveness to community participation reinforces the feeling that viewer involvement genuinely influences the direction of the investigation, creating a collaborative experience rather than a strictly pre-routed narrative.
Hopes For Future ARGs
Interloper is my favorite ARG so far, and nothing else has come close to it.
It stands out by presenting a grounded mystery built from familiar Source engine concepts and mechanics. The series becomes disturbing by subtly twisting things players already recognize from Half-Life and the Source engine. As a result, its realism creates deep immersion while also introducing unfamiliar ideas hidden within familiar systems.
That said, this ARG resonates most strongly with viewers who have spent time playing Source engine games or enjoy tinkering with games at a technical level. Much of its impact comes from recognizing what feels normal before it slowly becomes unsettling. While newcomers can still find it interesting, this may explain why Interloper never reached the same level of popularity as ARGs like Petscop. I likely represent the former group, having spent so much time with Source-based games.
What Interloper ultimately represents is a direction ARGs could lean into—one that complements viewers through interactivity, reactivity, and realism. By adapting existing games and twisting them into complex mysteries without breaking their internal logic, it demonstrates how familiarity can be a powerful foundation for immersive, participatory storytelling.
I’m glad to see newer projects on YouTube exploring similar ideas, such as the Minecraft ARG by Avery or Parabox by Valve Documentaries. These series also twist our understanding of familiar games, though they currently lack the same level of interactivity.
Ultimately, I hope more ARGs follow Interloper’s approach by embracing deeper interaction and participation.
Because, you know, analogue horror becomes increasingly mainstream, and we’re pretty hungry for something fun and new. Cheers.