Roll over vs. roll under
Exploring roll over vs. under systems and Mothership RPG
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In the past we’ve looked at opposed rolls in board games and roleplaying games. This included some discussion of modifiers, ties, and examples such as Oath.
This week we are exploring a similar topic: roll over vs. roll under dice systems!
And also how Mothership RPG uses them…
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Roll over vs. roll under
In both roll over and roll under systems, players usually roll dice, add or subtract modifiers, and then compare that result vs. a target number:
Roll over: If the result is equal to or higher than the target, it is a success.
Roll under: If the result is less than the target, it is a success.
A simple “roll over” example would be rolling vs. an action’s Difficulty Rating (DR) in MÖRK BORG. You roll one twenty-sided die (1d20) and compare it to the DR associated with the action (6 = easy, 16 = really hard). If what you rolled was equal to or greater than the DR, the attempt was successful.
Other systems, such as Emberwind RPG use roll under. You need to roll under (i.e. less than) your character’s relevant skill to succeed. The higher the skill, the better your chance of success.
Dungeons & Dragons uses (for the most part) a d20 roll over system, meaning higher numbers are better.
An unscientific poll
I recently ran a poll asking, “Do you prefer roll over or roll under systems in your tabletop games?”
With 54 votes, the results were as follows:
With such a small sample size, I’m inclined to think that roll over, roll under, and doesn’t matter were all about the same.
But perhaps there is a slight preference for roll over. A Reddit poll (N=172) showed 72% favored roll over and 28% preferred roll under. There was no option for both/neither.
Is there a way to determine if one method is better than the other?
In support of roll over
The question about roll over vs. roll under comes up regularly, and there has been much debate on this topic.
Here are some of the most frequent points in support of roll over:
People like rolling big numbers: It’s easier to understand that “bigger is better” and the results are more “intuitive.”
Many people are familiar with Dungeons & Dragons: The concept of “rolling a 1” and “a nat 20” are fairly well known. This can supposedly make it easier for new players to understand the game.
Exploding dice are fun: In “higher is better” systems you can do things like exploding dice. When you roll the highest possible value, you roll it again and sum the values. This gives you a (small) chance of getting really high results!
Easy to change the difficulty: When you are rolling vs. a target number, the higher the target number the more difficult the task. This might make more sense to new players and can be easily adjusted.
Better at representing impossible tasks: In a roll over system, it’s possible to set a target number that is impossible to achieve (e.g. roll 1d20 to beat a DC=30). This can be a problem in a roll under system because almost all dice include a 1 on them, making every task at least a little bit probable.
In support of roll under
There are also some points that routinely come up in support of roll under systems:
Reduced need for modifiers: Many roll under systems can remove modifiers and extra target numbers. This can reduce the amount of math required before the roll. Rather than having a skill that gives you +2 to a roll vs. a target of 15, and having to add and then compare, you can usually just try to roll under the target.
Higher skill numbers are better: When rolling under vs. your character’s skill, it might make more sense that a higher skill number makes you more likely to succeed. It also allows progression of skills to go from low to high.
Percentile dice make probability clear: When using percentile (d100 or 2d10) dice, roll under becomes a transparent way of showing the chance of success. If your target is 60, and you need to roll under that… you have a 60% chance of success.
Sense of player control: It might be hard to define, but in many roll under systems the player rolls a die vs. their own skill. They “control” both the roll and the target value. This is different than a roll over system where the game master is setting a difficulty target for them.
Just be consistent
A significant number of people seem to disagree that this is even a valid question. There is no “better” system. Roll over and roll under are just two ways to solve a problem. The important part is to be consistent.
If you choose roll over or roll under, stick with it. It’s when you start to mix both in the same system that it becomes confusing. You roll under for somethings, and have to roll over for others. Are higher numbers good or bad? I rolled a one, is that good?
This potentially increases the mental load on players.
But here’s a counter-example…
Mothership RPG
One reason I’ve been thinking about this lately is that I’ll be running Mothership RPG for the first time this coming weekend. Having never played before, it’s been a pleasure reading through the Warden’s Operation Manual and Player’s Survival Guide.
In general, Mothership is a roll under d100 system with some exceptions:
Stat checks: Mothership stats (e.g. Strength, Speed, etc.) can be 27 - 65 to start. When attempting an action, players roll d100 vs. the relevant stat. Rolling less than the stat is a success, otherwise it’s a failure.
Saves: Mothership saves (e.g. Sanity, Fear, Body) start at 12 - 50. Similar to stat checks, when making a save, players roll d100 and need to be under their save number.
Each of these can be modified with advantage or disadvantage to make the chance of success better or worse. In addition, rolling doubles (i.e. the same number on both dice) results is a critical success or failure. Rolling doubles under the target is a critical success and rolling doubles over the target is a critical failure.
In both stat checks and saves, rolling lower is better.
Stress and panic checks
Here is where Mothership appears to break the rule of “just be consistent” when it comes to roll over vs. roll under systems: panic checks.
Each time you fail a stat check or save in Mothership you gain one point of stress. Throughout the game you are bound to fail attempts, and will gradually increase your stress, though there are some ways to reduce it.
Any time the player rolls a critical failure on a stat check or save, they must make a panic check. To do so, they roll 1d20 and compare vs. their current stress. They succeed if they roll higher than the stress, and fail if they roll equal to or less than their current stress.
There’s a table of panic effects which correspond to the failing die roll, ranging from Jumpy at 3, Haunted at 12, and up to Heart Attack at 19.
This mixes the roll under system of stat checks and saves with the roll over system of panic checks.
Isn’t that what we determined was the wrong way to approach this?
Mechanisms that support the theme
Back when we explored opposed rolls, one of the things to think about was this:
Think about how the mechanism fits the context of the game. Opposed rolls might fit well when there are two parties in direct opposition, while target numbers might fit better for a player versus the environment (or themselves).
I think Mothership is doing exactly this when blending both roll over and roll under.
The roll under stat checks and saves allow for easy rolls, little math, and a skill progression that goes from low to high. Higher skill numbers are better. The player controls the dice and the target number.
The panic checks, however, are more rare and intended to be special. The books even suggest calling the d20 used The Panic Die, rather than just another die from your bag. Stress is accumulated throughout the game, and it increases over time, as you would expect. More stress (i.e. a higher number) is a bad thing.
Does mixing the two systems add a bit more confusion or mental load? Perhaps. But does it also create a system that makes sense thematically, and is therefore more consistent? I would say so!
As mentioned above, I’ll be playing (and running) Mothership for the first time this coming weekend. It was one of the top “what TTRPG do I need to play” responses in the most recent Skeleton Code Machine Reader Survey, so I’m really looking forward to it! Watch the Recently Played section of Exeunt Omnes for my post-play report.
Conclusion
Some things to think about:
Know when to break the rules: It’s easy to read game design articles and books and mentally build a list of rules to follow. While they can be helpful guidelines, many of the best games break many of these rules. Don’t be afraid to do what you want.
Questions without an answer still matter: While I would agree that there ultimately isn’t a clear winner between roll over and roll under, it’s still worth thinking about. There are advantages and disadvantages to each, and there is always something to learn from how each game uses them.
Mechanisms that support the theme: As we saw with Inhuman Conditions and Opposed Rolls, mechanisms can be implemented in a way that makes sense in the context and theme of the overall game.
I need your help! I’m running my first ever Mothership game as a one-shot. One player already did Another Bug Hunt, so would prefer something else. Which adventure module should I use? Tips, advice, and encouragement welcome in the comments!
— E.P. 💀
P.S. Need a CY_BORG heist? Check out Blackflower!
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The micro-game at the end of every post is roll-under. :)
I used Haunting of Ypsilon 14 as an intro and it worked great. Very focused, simple, thematic. For the modules mentioned, either Dead Planet or A Pound Of Flesh but both are bigger with many options and bigger 'playgrounds' that can support a full-on campaign and require much more reading than Ypsilon. I've read and run some of all 3.