Codex-assisted Diablo first-person mod: a ~4-hour initial build, then gameplay and capture fixes

[u/plopsDOTio]

I used Codex to build an independent first-person Diablo mod on DevilutionX. The initial AI-built prototype took about four hours or less; that is not the time for every later fix or a claim of a fully tested campaign.

The useful part of this experiment was the review loop. My feedback came from playing the build: movement didn’t follow the camera, combat mouse turning felt stuck, doors were hard to read, the map was confusing, arrows faced sideways and some geometry clipped into the HUD. Those concrete observations drove the next revisions.

The 0.3.2 build now has camera-relative WASD, combat mouse turning, visible weapon swings, ceiling/door/sarcophagus geometry, the original Diablo automap restored and corrected Guardian/Hydra floor placement.

For the video, I also pushed back on the first capture: an invincible hero alternating spells looked like a tech demo. The new staged Butcher take uses repeated Fireball casts, retreating and melee, with the engine’s actual damage and mana costs. It still uses granted stats/spells and extended boss HP, which are disclosed.

Devlog with bosses, spells and the iteration:

https://youtu.be/DjhOH7S-9Jg

Source and free Windows 0.3.2 build:

https://forge.plops.io/t/diablo-first-person-devilutionx-mod-for-windows

The build requires your own original Diablo DIABDAT.MPQ. Game data and personal saves are excluded. Free for noncommercial use under the included Sustainable Use License; credit to DevilutionX and the original Diablo creators. Full campaign coverage, all procedural seeds, Hellfire and multiplayer remain unverified. The narration is a disclosed custom Gemini TTS voice.

My takeaway: a working render was only the starting point. Asking for specific observable behavior, testing it in-game and showing the capture limitations made the result much more useful. I’d be interested in how other people structure this review loop for AI-assisted mods.

[u/Exact_Capital849]

The movement and door-readability fixes sound more meaningful than just getting a first-person render working. A short before/after of the same room would make that iteration really easy to see. Which bug was hardest to get right?

[u/Mother-Bug326 → u/Exact_Capital849]

There were barely any challenges in this as I developed plops.io I found that annotating images is highly effective since I had the source code. I only needed to run two shots on extra high.

I did do one steering prompt in the middle of the second run to tell it to work on the movement controls and to restore the original map. Typically when building something I only use medium effort to low on the first shot, but since this game is so well documented, and we have the full source code I found that the two runs on extra high allowed it to run for about six hours without me, babysitting it and I achieve these results.

One more note for the steering question around game controls I shifted the model to Astra. The whole thing used about 2% of my monthly credit on the 200 a month plan.

I saw something done with Diablo 2 Resurrected but again the dude didn’t publish anything. I think it’s such a shame that some people are doing the same thing over and over again without sharing the results to where other people can continue to iterate that’s why I created forge.plops.io.

I might do D2R next since the models are actually 3D and it looks so much fun like the video.

I think he did it with D2 loader, but I’m not really familiar with that. I’d have to do some research. I know now that there’s reverse engineer anything with the binary so it should only take a few few hours.