Aliens: Colonial Marines – How to Fix AI

The AI in Colonial Marines is a mystery, but I’m here to finally shed some light on it.


This short guide was written specifically to help people understand the Colonial Marines AI, and try to fix some of common bugs associated with it. Contrary to popular belief, the AI in Colonial Marines isn’t really all that bad, it’s just misunderstood.

This guide is to help dispel some of that mystery.

Difficulty Scaling

First off, let’s discuss the huge mystery of difficulty scaling. The AI in Colonial Marines is subject to a scaling system, the difficulty increasing subtly based on gameplay. The gameplay element in question here seems to be a rating based on difficulty played, XP gained, enemies killed, or levels completed, within a 24 hour period. Possibly all of the above factors, possibly only one or a few. The gist is, the more you play, the harder the game gets. After 24 hours, this scale resets to zero.

Each player has their own difficulty rating that effects the scaling, and it’s multiplied by the number of players in a coop server. The overall difficulty setting itself has a rating, such as Ultimate Badass or Hardened. So, here’s a super basic equation to help explain:

Scaling = Difficulty Level x Player Rating x Number of Players

  • Scaling: How hard the AI enemies are.
  • Difficulty Level: The difficulty level the host chooses.
  • Player Rating: The amount a player effects the scaling, based on how much they’ve played in 24 hours.
  • Number of Players: The number of players in a server, max of 4.

The scaling has a cap. The player rating also has a cap. So a game can only become so hard even on Ultimate Badass, but it’s definitely a huge factor in gameplay. This is the number 1 reason people have a hard time understanding the AI behavior.

The “Teather” Typo Bug

It’s somewhat commonly known by now that there’s a typo in the PecanEngine file located here:

  • Documents\My Games\Aliens Colonial Marines\PecanGame\Config

This line specifically:

ClassRemapping=PecanGame.PecanSeqAct_AttachMarineToTether -> PecanGame.PecanSeqAct_AttachPawnToTether
ClassRemapping=PecanGAme.PecanSeqAct_AttachXenoToTether -> PecanGame.PecanSeqAct_AttachPawnToTeather

Well, it’s been speculated that this typo could have huge ramifications on the AI. Now, personally I’ve not seen huge evidence in the AI behavior to support this myself after a lot of testing, but most people recommend doing it. So I do it too.

It’s recommended to change the bottom (xeno) line to:

ClassRemapping=PecanGame.PecanSeqAct_AttachXenoToTether -> PecanGame.PecanSeqAct_AttachPawnToTether

Supposedly, this helps AI xenomorphs with pathing behaviors.

The Memory Budget Placebo Effect

A lot of people talk about editing the values of the memory budget in the PecanEngine file, and how it may have an effect on the behavior of the AI. Here is that section fully default.


I’ll be clear: it does not influence the AI.

After a boatload of testing, there is no reason to believe these values even effect the game at all.

The Idle Xenomorph Bug

This one is subject to A LOT of speculation, myself included.

The basic gist of the bug is that xenos will get stuck mid path and just stand idle and unresponsive. Nobody knows exactly what causes this bug, or how to fix it. Many have tried to fix it using memory budgets, as mentioned above, and mods of various kinds.

I’ve been doing a lot of testing, and have some theories how to at least mitigate it:

  • Set the game to run in Windows XP Service Pack 3 compatibility mode. This seemed to make the game run better in general.
  • Use a patch, such as Large Address Aware, to allow the application to use 4 gigabytes of RAM. Colonial Marines is a 32 bit application, meaning it can only use 2 gigabytes of RAM at a time. Allowing it to use 4 essentially makes it a 64 bit application, and potentially less likely to crash or have issues.
  • Disable Framerate Smoothing. This one is kinda experimental. Framerate Smoothing is a setting in the PecanEngine file that essentially caps the game at 62 fps. This is not necessarily a bad thing, but a higher framerate may give xenos more time to break out of the bug? I don’t recommend it, but it’s a suggestion.
  • Do NOT, and I mean DO NOT, use Nvidia control panel to manually force anti-aliasing. The game really breaks itself when you use MSAA for some reason. I recommend using the Nvidia Profile Inspector program to set FXAA and SMAA instead, because they don’t cause these issues.


While the AI in Colonial Marines might not be the most outstanding AI ever written in human history, it’s definitely not nearly as bad as people act like it is.

Hopefully this will help some people to understand and patch up their AI and make the game more enjoyable for them.

Helena Stamatina
About Helena Stamatina 2689 Articles
My first game was Naughty Dog’s Crash Bandicoot (PlayStation) back in 1996. And since then gaming has been my main hobby. I turned my passion for gaming into a job by starting my first geek blog in 2009. When I’m not working on the site, I play mostly on my PlayStation. But I also love outdoor activities and especially skiing.

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