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The Five Variables of a Core Dice Mechanic That Matter
A core dice roll is a bundle of variables that shape how a game feels, how players assess risk, and how much work the GM has to do. This post breaks down the five big factors inside the dice loop: who sets the target, what shape the randomness takes, how odds get modified, how outcomes are interpreted, and when you should actually roll in the first place. Each of these choices changes tension, pacing, tone, and player responsibility.
By JimmiWazEre
Opinionated tabletop gaming chap
TL;DR:
A core dice roll is a bundle of variables that shape how a game feels, how players assess risk, and how much work the GM has to do. This post breaks down the five big factors inside the dice loop: who sets the target, what shape the randomness takes, how odds get modified, how outcomes are interpreted, and when you should actually roll in the first place. Each of these choices changes tension, pacing, tone, and player responsibility.
Introduction
Last time we talked about what a core dice mechanic is, so today we’re going to dive into the five variable elements of a dice loop to dissect what happens between the expression of player’s intent and the result, and then why so many systems seemingly reinvent it.
Get yourself a cup of tea for this one, there’s a lot to unpack here.
The Dice Loop
Quick refresher first for those at the back: what do I mean when I talk about dice loops? Well, I’m talking about the four stage process that happens whenever you engage in the core mechanic. Specifically:
1. Action declared
2. Variables Applied
3. Dice Rolled
4. Consequences Interpreted
This post drills into everything that happens between declaring the action and reading the outcome. That is the variables that shape odds, difficulty, and tone.
Variable 1 - What Are We Rolling Against, And Who Decides?
Whether you call it the DC, TN, AC, or number of successes, this variable is simply the target you need to beat. Different systems decide that target in different ways, and that choice carries a lot of weight.
Some games put the decision in the GM’s hands. In 5e, for example, the GM sets the DC, which gives them fine control over difficulty but also creates a subtle conflict of interest to manage: you want the players to succeed, but you also want the challenge to feel meaningful. On top of that, every judgement call adds to the GM’s mental load, which is already stretched thin.
Other systems remove that burden entirely. In GOZR, for instance, the GM doesn’t set a difficulty at all — the “target” is simply the relevant character stat. That strips out GM bias and keeps the load light, but also means the GM can’t tune difficulty moment to moment.
Therefore this choice changes the feel of the game. Rolling against fixed values gives players more meta-knowledge and puts responsibility for risk firmly in their hands, encouraging calculated decision-making. However, when the GM sets the target instead, players may feel the GM shares responsibility for success or failure — which is why you often hear GMs say things like “I killed my player last session.”
Variable 2 - What Shape Does Randomness Take?
You can also radically impact the game by what the game has you roll, due to the way different combinations of dice affect results distributions.
Single Dice
A single dice, take a d20 for instance, has a 5% chance of landing on any given result. For this reason, single dice rolls can feel swingy as the range of possible outcomes is equally likely. This is part of why 5e feels “heroic” - massive rolls are not uncommon in comparison to other results, and there’s a good chance of getting a stunningly high roll at any given time. In isolation it also contributes to comedy goofy moments where massive failure is also a very realistic prospect.
Multiple Dice
However, if you roll multiple dice and combine the score, then you’re in a bell curve distribution situation where the final result will heavily favour the median possible outcome, and outcomes at the extreme success and failure ends will be significantly rarer. This has the effect of making the game more predictable, and therefore gives the player more ownership over the outcomes they generated. It works well for games with high lethality because players can predict odds more reliably:
2d6 result | Odds
2 or 12 | 3%
3 or 11 | 6%
4 or 10 | 8%
5 or 9 | 11%
6 or 8 | 14%
7 | 17%
Dice Pool
If you have a dice pool system, like in AlienRPG where each result of 6 is a success, in that circumstance each dice added to the pool increases your chance of obtaining at least one success, but the impact on the odds that each new dice added to your pool shrinks massively with each new dice added via diminishing returns:
Dice | Odds | Increase
1d6 | 17% | +17%
2d6 | 31% | +14%
3d6 | 42% | +11%
4d6 | 52% | +10%
5d6 | 60% | +8%
6d6 | 67% | +7%
7d6 | 72% | +5%
8d6 | 76% | +4%
This type of system is good for capping the ability of player characters within a certain range, keeping abilities grounded which is important for systems where you want your players to never feel invulnerable.
It’s undoubtedly true that rolling big handfuls of dice is not only fun, but also that fraction of a second you spend sorting through the results hoping for a success is tense.
Variable 3 - How Do We Modify The Odds?
This works very closely with variable 2, because different dice methods of generating RNG present us with different options for modifying those rolls.
Additive Modifiers
A common method to change the odds of a roll is to use your character’s derived stats and “add your modifiers” to the result of the roll. This is clean and intuitive from a simplicity standpoint, but in doing so, it takes certain low results off the table completely. For example, a 5e Rogue with a +9 in stealth is never going to score less than 10 on their roll (we’ll talk about critical fails in a bit) and that’s a problem, because now our modifiers have moved beyond adjusting the odds toward creating certainty and in doing so risks undermining the purpose behind having a core dice mechanic in the first place.
If you want to create a game where the players can indulge in a power fantasy, this is the route to take.
Dice Chains/Step Dice
Rather than giving players a bonus of an absolute value to add to their dice roll, dice chains and step dice elect to give them a different sized dice instead. Let’s assume that you want to roll high - in this case, a character rolling a d6 is capped out at 6, vs. a character rolling a d12 is capped out at 12.
The potential of the d12 character is therefore twice that of the d6 character, but we’ve avoided creating certainty, as a d12 can still roll low. So instead of narrowing the result range as with additive modifiers, step dice grow or shrink the entire results band upward or downward.
This works well where we want to give players meaningful variances in ability without turning their characters into unbeatable demi-gods, but it does make dice rolls slightly less intuitive. Who hasn’t had that player that asks every time about what dice they need to roll, even when it’s always a d20? This will probably exacerbate that problem!
Advantage/Disadvantage
Advantage/disadvantage is one of the simplest difficulty tools you can give a GM: roll twice, keep the better or worse result. It shows up in different forms across systems, but the core idea is always the same.
There’s a lot to like about it:
It’s clean. No maths, no modifiers, no lookup tables.
It’s emotional. Players immediately feel the stakes when the dice leave their hand a second time.
It’s universal. You can bolt it onto almost any core mechanic without breaking anything — d20, roll-under, step dice, dice pools, whatever.
But it’s not flawless.
Firstly, the maths isn’t intuitive. Rolling twice feels like a small nudge, but in a d20 system advantage is worth roughly a +3 to +5 bonus depending on the situation which can be bigger than many GMs intend. The reverse is true too. If you don’t know the underlying probability shift, you may end up modifying odds more aggressively than you realise.
Secondly, it adds friction. You’re doubling the number of rolls, and while that sounds trivial, groups who rely on this mechanic heavily might notice the slowdown, especially at tables where players already hesitate or re-check dice.
For those reasons, the only time I’d avoid using advantage/disadvantage is when the system already has too many levers to pull. If you’ve got static modifiers, step dice, DC adjustments, and situational tags all competing for attention, adding another knob to twist just dumps more cognitive load onto the GM and makes it harder to stay consistent.
Variable 4 - How Do We Measure Outcomes?
Binary
Essentially we have three options. Firstly, we could argue that it is purely binary - the roll resulted in either a success or failure. This is clean and simple for sure, but it does not lend itself well to interesting outcomes, or keeping the game moving forwards. We’ve all heard the advice that as a GM, you should try to avoid saying “no”, well that’s what a failure is in this circumstance - it’s “no”. The problem is that it’s shut down an avenue of progress without opening up an alternative.
On the plus side though, it’s light on GM load. There’s nothing difficult about interpreting a binary result, and it’s clean and fast, and there’s less chance of the players feeling like they’ve been victims to some unanticipated gotcha.
GM Fiat
The second option creates GM load in the extreme, and opens you right up to conflict of interest: There is no codified success or failure - the GM simply interprets the strength of the result and assigns a suitable outcome to it based upon fiat, circumstance, and vibes.
GM fiat isn’t an official mechanic, but it becomes a de facto one when rules don’t specify degrees of success - you’ve seen it in action when the GM calls for a roll, you score a 4 and everyone at the table understands intrinsically that you’ve failed, yet the GM sort of awkwardly goes on to award you a success of sorts because failure wouldn’t have made sense.
It’s only really an option for non dice pool mechanics though. No one would be able to get away with witnessing a dice pool result of zero successes and then contorting that into a limited success!
Degrees of Success
This option is a middle ground. In this system the game has some codified way of defining outcomes more than yes or no. Typically opening up to:
yes and
yes
yes but
no but
no
no and
Now different mechanics will allow this in different ways. With a dice pool, it might be that you strengthen the outcome with the more successes you roll. With other systems they break possible dice results down into ranges, either according to absolute values (such as 1 below TN) or percentages (such as 10% below TN) and then transpose the list above to those ranges.
We’ve seen this applied to great effect in games like Call of Cthulhu where the ranges regular, hard, and extreme are mapped to a percentage over or under your stat, or Powered by the Apocalypse, which favours absolute values.
Critical Hits
Critical hits are a wildcard baked into many core mechanics; that sudden spike of drama when the dice explode, double, or land on that one special result. In design terms, crits are a way to break the expected curve, injecting moments of swinginess into systems that might otherwise feel predictable.
The simplest form is the classic natural 20 in D&D: roll the highest face on the die and you get a bigger, flashier result. What’s important is that this happens regardless of modifiers. Even a clumsy novice can occasionally land a perfect blow, and even an expert can fumble catastrophically. Crits flatten the power curve in tiny unexpected moments, and as a consequence they’re exciting.
Different systems spin this idea in different ways, and they tell you what sort of game you’re playing:
Linear dice systems (like d20 games) produce crits fairly often because all outcomes are equally likely. This reinforces the “heroic swinginess” the d20 is known for.
Bell-curve systems (like 2d6 or 3d6) make crits rare and meaningful, because the extreme ends of the curve hardly ever come up. You’ll still occasionally roll a double six or triple six, but it’s much rarer and less reliable.
Dice pool systems handle crits by counting multiple successes, matching numbers, or converting high results into special effects. This lets crits scale with character competence: more dice rolled equals more chances to spike, but still without guaranteeing it.
Exploding dice create a different flavour of critical entirely: every max roll triggers another roll, allowing theoretically infinite results. I use them when I play D&D because it kind of represents the lowly peasant hitting the dragon in his eye with an arrow.
Under the hood, critical hits interrupt the normal flow of risk and reward. They’re a “spike of possibility” that keeps players hoping, even when the odds aren’t in their favour.
Variable 5 - What Justifies A Roll?
Of all the variables in the dice loop, this one is the most misunderstood: when should you roll at all? It sounds trivial — “roll when there’s uncertainty” — but in practice, this decision shapes the entire pace, tone, and feel of a system far more than most people realise.
I’ve written about this before in my older post (Do You Call For Too Many Rolls?), but it’s worth pulling back into this series, because it turtley belongs on the list of core variables.
A game that rolls sparingly feels empowering, deliberate, investigative, even cinematic.
A game that rolls constantly feels random, procedural, or punishing.
A game that leaves it vague risks becoming muddled, inconsistent, and exhausting for the GM.
Conclusion
Well done, you got to the end! Honestly that one was a lot of work and took ages to write up, so I hope it proves useful to all the TTRPG dice nerds, academics, and designers out there. If you didn’t catch the first post in this series, you can check it out here, and stay tuned for the next piece on what mechanics work well with different tones and genres.
Hey, thanks for reading - you’re good people. If you’ve enjoyed this, it’d be great if you could share it on your socials - it really helps me out and costs you nothing! If you’re super into it and want to make sure you catch more of my content, subscribe to my free monthly Mailer of Many Things newsletter - it really makes a huge difference, and helps me keep this thing running!
Catch you laters, alligators.
6 Games that nail What Rules-Lite TTRPGs Should Be
A good rules-lite system doesn’t overwhelm you with procedures and crunch for every situation. Instead, the key procedures are covered and it gives you a clear, concise core mechanic. Then it trusts you to apply it flexibly.
By JimmiWazEre
Opinionated Tabletop Gaming Chap
TL;DR - Rules-lite isn’t the same as rules-incomplete or rules-inconsistent. Don't conflate them.
This post contains affiliate links.
Introduction
I want more people to play Rules-Lite games, but this crusade of mine is hindered by a misconception of what a rules-lite game actually is.
A lot of people hear "rules-lite" and think "lazy" or "half-finished." But that’s missing the point entirely. A great rules-lite RPG isn’t undercooked, it’s efficient, elegant, and focused. Let’s unpack what makes a minimalist system actually good, and why "less" doesn’t mean "worse."
What Is Rules-Lite
A good rules-lite system doesn’t overwhelm you with procedures and crunch for every situation. Instead, the key procedures are covered and it gives you a clear, concise core mechanic. Then it trusts you to apply it flexibly.
It’s just like that old saying:
Give a GM a fish, and they can run a session. Teach a GM to fish, and they can run a campaign.
Or something like that. I don’t know, it's close enough.
What isn’t Rules-Lite?
Let’s be crystal clear, rules-lite is very different from rules that are simply incomplete or inconsistent.
Inconsistent rules happen when a mechanic is explained more than once but the explanations don’t match. This usually signals a rushed edit. One version may or may not have replaced the other, but both made it to print. That’s not planned ambiguity, rather it comes over as just poor proofreading.
Designers: please, if someone flags this, don't try to convince us that you’re providing options. No one's falling for it, just own it and issue a FAQ or errata.
Incomplete rules are when a mechanic is introduced but not fully defined. For example, a game might explain how to hit an enemy in great detail… but never actually explain how damage works. You can’t convince me that this is minimalist design, it's just frustratingly half baked rules - because now we know that there is a specific way that this should be done, but we’ve no idea what it is.
RAI Matters
It all comes down to understanding the Rules as Intended (RAI). If the designer has said enough to give the GM an understanding of the game’s core rules language, then the GM should be confident that they can make a ruling that falls in line with RAI. If not, flesh it out some more.
Gameplay examples are great for this, as are developer commentaries in the sidebar. Designers take note!
Experience matters
I'm a big fan of the rules-lite philosophy, but if you've never run a TTRPG before, there is a danger that you might not have developed that muscle yet which allows you to make rulings up on the spot that feel consistent with the game system. Just bear that in mind before you pick your first game.
That’s not to say that a rules'-lite game shouldn’t be your first, but rather that I just want to make sure that your expectations are managed. It may start difficult, but it will get easier as you go on.
Recommendations
If you’re interested in picking up a good rules-lite game, then I’ve got a short curated list for you of some of my personal favourites. Full disclosure though my dudes, some of these are affiliate links, and if you chose to pick one up using the links provided, then I’ll get a small kickback at no extra cost to you.
Mausritter
Mausritter is a charming, rules-lite fantasy RPG where players take on the roles of brave little mice in a big, dangerous world. Built on Into The Odd, an OSR style framework, it uses simple d20 roll under mechanics and item slots for inventory, making it quick to learn and run. Its elegance lies in its ability to deliver rich, old-school adventure vibes with modern usability and 1990’s Disney cartoon flair.
I played in a duette game of this with my wife at the kitchen table, and she really enjoyed the vibes. With tweaks to the lethality I can see this being really popular with young families too.
Index Card RPG
ICRPG strips tabletop roleplaying down to its essentials with fast, flexible rules that encourage creative problem-solving and dynamic pacing. Everything runs off a single target number per room or scene, making it intuitive and highly adaptable. Its modular design and DIY ethos make it perfect for GMs who like hacking and building custom worlds on the fly.
EZD6
Created by DM Scotty, EZD6 lives up to its name with a system that’s incredibly easy to pick up and play. Most rolls come down to a single d6 against a target number, streamlining gameplay while leaving plenty of room for dramatic moments. It’s especially good for narrative-driven groups who don’t wanted to be limited by predefined abilities on their character sheets, and instead want to freedom to narrate their abilities as they see fit.
One of my players who’d never GM’d before in her life ran a couple of us through a homebrew adventure using this system and it was an absolute blast.
Pirate Borg
Pirate Borg is a brutal, rules-lite game of swashbuckling horror on the high seas. Inspired by Mörk Borg, it mixes fast, deadly mechanics with punk rock layout and evocative setting material. It’s ideal for players who like their pirate adventures with a side of doom, decay, and dark magic, and who don’t mind their characters dying spectacularly.
The squint-and-it’s-historical side of this game has literally made me buy pirate history books and start listening to pirate podcasts. I love all that stuff now, and it takes me back to my childhood - playing Secret of Monkey Island on my big brother’s Amiga. Good times.
GOZR
GOZR is a wild, gonzo sci-fantasy RPG that feels like it escaped from the back of an '80s metal album cover. It runs on a straightforward d20 roll-over system and embraces weirdness at every turn, from its mutant characters to its DIY zine-style aesthetic. It's brilliant for groups who want something fresh, funky, and full of chaotic creativity without a ton of prep.
I also wrote an opinion piece for this game a few months ago which included a free system cheat sheet that I’d worked on with the help of the games designer to get players started sooner. Can’t recommend it enough!
Spellz!
Indie developer, Jake Holmes recently reached out to me on Bluesky with an interesting little one page rules-lite game he was working on called SPELLZ! The game is still in it’s beta testing phase and he’s taking feedback on it it, but for the price of totally free, and for the sake of reading less than a single page - it’s definitely worth a look in if you want to see just how lite the rules can go!
It’s a fast TTRPG where magic is improvised in real time using letter tiles. Players draw tiles and try to form words on the fly — the word they create becomes the spell, and its effect is narrated accordingly. Stronger or stranger words often have bigger effects, and failed spell attempts can backfire spectacularly, with the GM repurposing your discarded letters.
I’ve not played it, but I have given feedback on the rules which was promptly actioned. It looks quick, and perfect for creative groups who enjoy thinking on their feet, might even be a way to introduce TTRPGs to your mum, dad, and nan who’s idea of a tabletop game otherwise begins with crosswords and ends with Scrabble!
Heya, just a thought, if you want me to take a look at your game and feature it on the site, like SPELLZ! Then drop me a message, lets have a chat!
Conclusion
The key message here is that if you've been frustrated by rules-incomplete or rules-inconsistent in the past, please don't be put off a rules-lite system because you're assuming it's the same thing. It ain't. If you get overwhelmed by books the size of a university textbook and you want to start small, rules-lite could be for you.
And so endeth the sermon.
Hey, thanks for reading - you’re good people. If you’ve enjoyed this, it’d be great if you could share it on your socials - it really helps me out and costs you nothing! If you’re super into it and want to make sure you catch more of my content, subscribe to my free monthly Mailer of Many Things newsletter!
This post contains affiliate links.
A core dice roll is a bundle of variables that shape how a game feels, how players assess risk, and how much work the GM has to do. This post breaks down the five big factors inside the dice loop: who sets the target, what shape the randomness takes, how odds get modified, how outcomes are interpreted, and when you should actually roll in the first place. Each of these choices changes tension, pacing, tone, and player responsibility.