No matter how much I love horror games, so many of them can suffer from the same issue: repetition diminishes tension. The first time I go through a sequence, it’s fraught with tension as I run for horrific monsters that surprise me from the shadows. But if I die at the final monster in a long sequence, I’m forced to repeat it. Suddenly, the tension of not knowing what’s around the corner is gone, and I’m just going through the motions until I make it to that final monster and try to overcome them. It’s easy to see the scripted nature of most horror games once you start repeating, taking away from the immersion required to truly ratchet up the tension.

Alien Isolation‘s most famous mechanic attempted to solve that issue. While the game does have enemies that perform prescribed patrols and scripted sequences, the Xenomorph is a different beast entirely. This creature has a systemic AI that is built to simulate one thing: being hunted by the Alien. As I wrote previously, this is one of the main elements that make Isolation feel like such an authentic representation of the original Alien movie. Not only does it capture the mood of its source material, but it helps alleviate the issues of repetition reducing the horror.

The YouTube channel AI and Games did a fantastic breakdown of how exactly the developers achieved this unique and ‘realistic’ AI. The AI controlling the Alien is divided into two main components: the “director” and the Alien itself. The director keeps track of the player, fully aware of their position and status at all times. The Alien itself is a reactive, sense-driven NPC that will react to the player’s actions when they are in its range. While the director commands the Alien, pushing it into directions to put it on a collision course with the player, it is never allowed to cheat and must always legitimately find the player through its senses. Its behavior is dictated by a 100 node behavior tree that is unlocked as the game progresses, giving the illusion that the creature is learning from each encounter.

The director also manages the “menace” of the game by measuring several factors about the relationship between the player and the Alien. These factors include proximity to the player, how long the Alien has been near the player, and how quickly it can reach the player. Once the menace reaches a certain level, the director sends the Alien elsewhere in the station, allowing the player some breathing room. This pacing that is done by the director is perfect for horror games, as sustained “menace” can become frustrating for the player, deflating the tension of the situation and replacing it with aggravation.

All of these pieces make for such a great experience in Alien Isolation, but they aren’t the only team to attempt to craft an experience like this. Left 4 Dead used a similar director to create unique enemy layouts each time. The AI in this game would place both enemies and items in varying positions based on each player’s current situation, status and location. Much like the Alien AI system, the director allows each playthrough of the game to be unique. Even upon starting the level over, you don’t know what enemies you’ll be facing or where to expect them.

A more recent example of a video game villain that relentlessly stalks the player is Mr. X from this year’s Resident Evil 2 Remake. While he stalks you for a smaller portion of the game than Isolation’s Alien, Mr. X definitely became one of the breakout elements that made the RE2 Remake so successful. Much like the Xenomorph, Mr. X has an AI that must search and find players in order to confront them. Running and shooting will attract him quicker, forcing players to alter their playstyle in order to avoid the unkillable creature. It’s a great mechanic that forces the player think about every encounter, weighing not only their resources, but whether or not killing certain enemies is worth risking the attention of Mr. X.

Even multiplayer games have structured themselves around this idea, replacing enemy AI with an actual player. Dead by Daylight and Friday the 13th have utilized this structure, casting one player as a killer hunting down the others. Evolve did a similar thing, with the players acting as hunters trying to track down and kill an ever-evolving monster. These games highlight just how important it is to create a horror experience where the player feels like they are being stalked by something with a true intelligence behind it.

Alien Isolation not only used its well thought out AI to replicate the feeling of the film, but also created a horror experience that maintains variety when replaying sections and creates a level of unpredictability not previously possible in games. Unpredictability is a key to keeping the horror fresh, always keeping you on your toes. Developers would be smart to try to craft systems like this, even for shorter games, as AI like this can really make you feel like there’s an actual monster terrorizing you rather than something that’s responding to a series of triggers.