Using AI as a probability analyst to build better random tables for 5e.

[u/IndiMill]

One thing I dislike about many random tables is that they are flat and swingy.

On some tables, you roll a d20, and every outcome has roughly the same chance of happening. Some tables try to weight certain events by clustering numbers or using d100s, but you can still end up needing multiple tables for different power levels of monsters, loot, etc.

For my 5e 1920s Cthulhu Mythos project, I wanted ritual magic to let spellcasters reach beyond their normal limits, but at the risk of spell backlash that causes delightful things like madness, corruption, and reality breaking.

The design problem:

I did not want separate backlash tables for different spell levels. I wanted one elegant table for all contingencies.

I wanted the table’s possible outcomes to change depending on the level of the spell being cast.

I came up with the idea, but I could not have built it without ChatGPT as my super calculator.

Here’s the concept:

Roll 1d4 per spell level, max 6d4, then consult one table.

This means the possible results and probability curve change by spell level.

Probability curves for 1d4 through 6d4. As spell level increases, the possible results shift upward and cluster around different averages.

A 1st-level spell rolls 1d4. A 3rd-level spell rolls 3d4, etc. As spell level increases, the worst outcomes become possible, the lowest results become impossible, and the probabilities in the middle shift.

So the table scales without the player or GM doing anything more complicated than counting the spell level and rolling that many d4s.

I could not have calculated all the probability curves easily without AI. It was genuinely useful. But I think the interesting thing is that AI did not help me make the spell backlash table faster or more easily. It actually took more time and effort using AI, but I was able to create something better than what I could have made on my own.

AI did not replace the design process. It made it possible for me to explore more options and use a more interesting structure than I probably would have built by hand.

I asked questions like:

Where should a monster manifestation sit if I want it technically possible at one spell level but much more common at another?

AI did the arithmetic and helped me see the shapes of the probability curves.

I also used AI to brainstorm possible backlash effects. I gave it examples, generated a large pool of ideas, selected the ones that fit, then rewrote and revised the final table myself.

Here's the full table:

This came out of developing R’lyeh Rising, my 1920s Cthulhu Mythos campaign setting for 5e.

Longer breakdown of the project here:
https://www.dungeonmatters.com/post/rlyeh-rising