# “Behind their simplistic behavior is a fairly elegant system.”

> Source: <https://unsung.aresluna.org/behind-their-simplistic-behavior-is-a-fairly-elegant-system>
> Published: 2026-08-17 15:23:57+00:00

For all these times we [talked about Super Mario](https://unsung.aresluna.org/tags/super-mario-bros/), we never covered another important game, Doom.

[Here’s a 17-minute video from decino](https://www.youtube.com/watch?v=f3O9P9x1eCE) explaining how the Doom monsters move and attack the player (the “AI” in the old sense of the word):

What’s really fun about this video is how it uses annotated source code (in contrast to Super Mario, the Doom source code was officially released and [open sourced](https://github.com/id-software/doom)), and particularly how it tasks the engine with explaining itself, setting sometimes elaborate stages just to show a principle or an algorithm – an absolutely perfect example of “show, don’t tell.”

decino has tons more of [these kinds of videos](https://www.youtube.com/@decino/videos) (click on Popular!), distinguishable by their yellow covers, if you want to pick another aspect of Doom that interests you.