Building a Better Spell Backlash System: TTRPG Table Design With AI

Part 2 in the Making of R’lyeh Rising Series

I use artificial intelligence in a variety of ways when producing TTRPG content. What is important is my philosophy: do not replace human thinking with lower-quality AI output. Instead, look for ways AI can enhance and complement human creativity.

For my new R’lyeh Rising 1920s Cthulhu Mythos 5e setting, I am going deep into exactly how AI was used during development through a series of “making of” articles. In this article, I am going to cover table design.

I do not like most random tables because they typically consist of a collection of outcomes that get worse or better as the number rolled increases, but with roughly the same odds of producing any outcome. That is fine when you want true randomness that does not scale with character level or adjust to the situation. However, I find that kind of design fairly lackluster.

How Is R’lyeh Rising’s Spell Backlash Table Different?

In R’lyeh Rising, spellcasters can use rituals to boost the power of their spells at the risk of suffering backlash. For the Spell Backlash table, I wanted to try something more ambitious than a list of equally likely random events.

What Is the Problem With Random Tables?

Random tables usually offer six, ten, twelve or twenty outcomes and ask you to roll the matching die. Every result has the same chance of occurring.

That is fine when all you need is a random answer. It becomes limiting when the possible outcomes should change based on danger, power, level or the situation. I think good tables should take those factors into account.

Random encounters are a good example. If one table serves both low-level and high-level characters, the weaker party can encounter something absurdly deadly while the stronger party can roll something completely irrelevant.

The usual solution is to create separate encounter tables for different level ranges. You can do the same thing for treasure, magical effects, environmental hazards and almost anything else that needs to scale. That works, but now the GM has more tables to keep track of.

For R’lyeh Rising, I Wanted Something More Elegant

A d100 table can look more sophisticated when the ranges are weighted. A common result can occupy twenty numbers while a rare result occupies only a few. That allows the designer to create a statistical distribution of outcomes.

Rolling 2d6, or two of any matching polyhedral die, can also create a natural probability curve. Results near the middle occur more frequently while results at the top and bottom remain rare.

These are both useful approaches, but neither solves the problem of needing different tables for different power levels. Even with a statistical distribution, a single traditional table is unlikely to produce meaningful results for both a 2nd-level and a 20th-level caster.

I wanted one table to rule them all, with possible outcomes and probabilities that changed based on the level of the spell being cast. It also needed to remain useful across the full level range covered in R’lyeh Rising, from levels 1 through 10.

This is where AI came in.

How Was AI Used to Create the Spell Backlash Table?

Some consequences needed to be completely impossible for weaker magic. Others needed to become more likely as the caster reached further beyond safe human limits. At higher levels, some of the mildest outcomes also needed to disappear.

Those requirements led me to an idea:

Roll one d4 for each level of the spell, then use the same table to determine the result.

The idea was mine, but AI helped me with the math.

How Ritual Magic Works in R’lyeh Rising

Ritual Spellcasting in R’lyeh Rising differs from the standard 5e or 5.5e rules. It allows a character to attempt to cast a spell one level higher than the maximum they can normally cast.

The ritual requires ten minutes of uninterrupted concentration. The caster then makes a spellcasting check against a DC equal to 11 plus the spell’s level.

If the check fails, the ritual fails and the spell slot is expended. If the check fails and the unmodified d20 roll is equal to or lower than the spell’s level, the caster suffers a Major Failure and rolls on the Spell Backlash table.

Most results are mild. Some are not. The most dangerous outcomes scale with the level of the spell being cast.

This creates a deliberate temptation. The character can reach beyond their normal limits to bend reality, but sometimes reality pushes back.

When backlash occurs, the player rolls 1d4 per spell level, to a maximum of 6d4, then consults one table.

The trick was getting the math right. The probability of rolling any given number on the table changes every time another d4 is added. Some lower results become impossible while new, higher results enter the realm of possibility. All of this happens on one table.

AI helped me calculate the probability distributions and arrange the outcomes so that, at each spell level, mild results were more common but more serious results became possible. The worst results could only occur at the highest spell levels.

The definition of a mild result could also change with the level of the caster. Summoning a creature from the void might be a deadly consequence for a 1st-level character but little more than a dangerous nuisance for a 5th-level character.

Spell Backlash Probability Distribution

Spell level	Backlash roll	Possible range	Average
1st	1d4	1–4	2.5
2nd	2d4	2–8	5
3rd	3d4	3–12	7.5
4th	4d4	4–16	10
5th	5d4	5–20	12.5
6th	6d4	6–24	15

The player only needs to count the spell level, roll that many d4s and add them together. The GM only needs one table.

The mechanics are simple, but the underlying probability structure is complex. It leads to a better table and more interesting results.

This is a way to make gameplay invisibly better. To make it work within a reasonable timeline, I needed AI’s help.

Using AI as a Probability Analyst

I did not ask AI to make a Spell Backlash table for me. I already knew the experience I wanted. My questions were about how the mechanic behaved.

How often would each total appear on 3d4, 4d4 or 6d4? At what spell level should permanent physical corruption become possible? Where could I place a manifestation so that it was technically possible at one level but more common at another?

AI calculated the combinations and helped place the outcomes in minutes. Without AI, it would have required a great deal of math, spreadsheet work and hours or days of patience. A math wizard might have been able to do this easily. I am not one.

AI handled the arithmetic. I made the design decisions.

AI also helped me develop possible outcomes. I provided an initial list of five examples to establish the flavor and style I wanted. I then asked AI to produce twenty more, followed by another twenty. After that, I requested variations on the ideas that were interesting but not quite right.

Eventually, AI had provided hundreds of ideas for me to consider. I selected my favorites, added them to the list of candidates, then rewrote and revised every one of them to fit my needs and the tone and style of the game.

AI became a thinking assistant, not a replacement for thinking.

What is interesting about this process is that using AI in this way made the table take more time to design than simply writing twenty outcomes, not less.

The result was also better.

I think this is a useful rule of thumb for working with AI. There are many situations where it can save time, but in game design, or any creative endeavor, saving time is not always the goal.

My favorite uses of AI are situations where it adds time to my process but allows me to explore ideas and techniques that would not otherwise be practical.

The Final Result: Spell Backlash in R’lyeh Rising

The finished table shows how the consequences progress from psychological disturbance to permanent corruption and reality-breaking catastrophe.

Spell Backlash Table

Spell Backlash Table

Roll 1d4 per spell level (max 6d4).

Roll	Outcome
1	Psychic Feedback. Roll for short-term madness.
2	Slug Gateway. Incapacitated 1d4 rounds as you vomit extradimensional slugs the size of sewer rats.
3	Reflected Agony. Take 2d6 psychic damage.
4	Whispers from Beyond. Disadvantage on Wisdom checks/saves for 10 min.
5	Minor Manifestation. Hostile CR 1 creature appears up to 30 ft. away.
6	Unwanted Attention. You feel something watching you. You cannot take short or long rests for 24 hours.
7	Inverted Outcome. Spell produces opposite effect.
8	Temporal Displacement. Vanish for 1d4 rounds while you live a lifetime in another reality. You gain flute proficiency.
9	Astral Echo. You glimpse the thoughts of an Outer Being. Roll on the indefinite madness table.
10	Sensory Bleed. You are blinded for 1d4 rounds as you see things that shouldn't exist. Roll for short-term madness.
11	Marked. Eldritch symbols appear on your skin for 1d6 days. Disadvantage on Charisma checks, except for Intimidation.
12	Dimensional Thinning. 1-in-4 chance a hostile CR 1 creature appears any time you cast a spell for 24 hrs.
13	Synesthesia. You see sounds and taste emotions. Permanent-2 to Perception checks.
14	Shattered Sanity. Roll on the indefinite madness table.
15	Haunted. A screaming spirit appears that only you can see. You have disadvantage on all rolls for 1 hour.
16	Physical Corruption. Permanent physical mutation. Disadvantage on Persuasion checks.
17	Psychic Devastation. 8d6 psychic damage. Auto-fail 1 death save if dropped to 0.
18	Changeling. A hostile CR 1 creature (GM’s pick) appears in your space, wearing your clothes. You vanish until the creature is destroyed.
19	Misdirected Effect. The spell affects you instead of the intended target. If you were the target, it affects your nearest enemy.
20	Moderate Manifestation. Hostile creature (CR = spell level) appears up to 30 ft. away.
21	Localized Catastrophe. 5d10 force damage in a 120-foot radius centered on the caster.
22	Waking Nightmares. Succeed on a DC 14 Wisdom saving throw or take 4d6 psychic damage at the end of each short or long rest for the next 5 days.
23	Existential Unraveling. Take 10d10 psychic damage. If reduced to 0 hit points, your soul is destroyed and replaced by a demon that exists solely to destroy your allies.
24	Major Manifestation. Hostile creature (CR 5 + spell level) appears 120 ft. away.

Separate tables could create similar scaling, but at the cost of more pages and more work for the GM. The d4-per-level system does all of it with one instruction.

The table is simple. The complex mechanics behind it are invisible.

How Can AI Make Game Designers Better?

Some research suggests that the people who benefit most from AI are experts in their fields. This raises an interesting possibility: the real advantage of AI is not replacing creative game designers, researchers or artists. It is enabling people with established skills and experience to reach higher and attempt things they otherwise could not.

Throughout the development of R’lyeh Rising, that is the approach I took to using AI.

I will share some of the other ways it was used in future articles in this Making Of series.

I covered art in the first article. Future articles will examine creature development, equipment design and playtesting.

About R’lyeh Rising

R’lyeh Rising is a 1920s Lovecraftian campaign setting for 5e, featuring new classes, creatures, spells, rules and adventures. Follow the Kickstarter pre-launch page to see more from inside the book.

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