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Game Design Masterclass – 2D20

I work for Modiphius on Dune: Adventures in the Imperium and Star Trek Adventures, so it’s no surprise I’m a fan of their 2D20 system. But its only recently with Dune that I’ve had to take a deep dive into the rules and noticed that 2D20 does a lot of things that make it more than worthy of an article.

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The 2D20 Concept

If you are not familiar with it already, this is the system used for pretty much all of Modiphius’ games, such as Conan, Star Trek, Infinity, Dune and many more. But I should add that it’s not used in the same way house systems were many years ago, with games crowbared into them regardless of whether they fitted or not. This is one of the first strengths of 2D20, it is exceptionally adaptable and each time it has been used it’s been tweaked and adjusted to fit the game setting, rather than the other way around. Cortex Plus (Smallville, Leverage, etc) is another system like this, making both more of a concept than a rules system at heart.

In 2D20, you get a base dice pool of (unsurprisingly) 2D20 to roll to beat a target number. This target number is made up from two attributes that are usually different for each game line, depending on its needs. Dune uses Drives and Skills, for Star Trek it is Attributes and Disciplines, for Conan it is Attributes and Skills. It really depends on what the setting requires, but the rules behind them are the same. Any die that rolls equal to or less than the target number is a success, and the more successes the better. Roll a 1 and that’s a critical, netting you 2 successes for that die. Additionally, if your character has a focus (a specialist skill that applies) a roll of less than one of the two attributes that makes up the target number will yield a critical too.

This means it’s possible to roll 0 to 4 successes on 2 dice, and the gamemaster sets a difficulty in successes to achieve the task. But the difficulty can range up to 5. This is where Momentum comes in, which is one of the other parts about 2D20 I really like.

Gaining Momentum​

If you spend a Momentum point on the test you can buy more D20s for your pool. The cost escalates the more you buy, and you can only ever have a maximum of 5 dice in your pool. While 2D20 isn’t the only game to offer ‘beanie points’ Momentum does have a few differences to what you are used to.

Momentum is gained by rolling more successes than you need. So, if the difficulty is 2 and you roll 4 successes, that’s 2 Momentum points to the group pool. Momentum can only go up to 6, so good rolls don’t make things silly. Momentum essentially represents what it is named after, the momentum your characters gain as successes build up in their actions, each leading to a better foundation for the next task.

Momentum is a quick and simple way to reward good dice rolls, and as it’s capped it encourages you to spend it. In most systems you are encouraged to hoard bonus points for when you really need them. But Momentum works best when you spend it freely and frequently. In fact, the system assumes some Momentum is being used on pretty much any roll, and spending it to overcompensate is a good way to regenerate the pool.

All this is leading up to my favourite thing, the difficulty 0 roll.

The Difficulty 0 Roll​

In 2D20 you can make a test with a difficulty of 0, that requires no successes to succeed. As this means an automatic success, you may be wondering why you bother rolling. In this case it is to see how much, if any, Momentum you can gain. But difficulty 0 tests are not just something for players to try and get free points with. They are a neat way to represent scouting out an area or asking around to gain information.

In plenty of games the PCs might arrive at a party and say “I’ll go around the room and see what rumours I can pick up” or something similar. Unless the GM has something specific in mind, you often end up shrugging or maybe granting a bonus later, or just making something up. But with 2D20 you can offer a difficulty 0 test and allow the PC to gain Momentum they can use in the scene later. It directly represents the advantage they have gained from asking around and checking out the surroundings. It might be spent later with the player referencing something their character heard or noticed in their initial investigation. “I’m buying an extra dice as I heard some gossip about this guy I’ll use when I challenge him.”

As much as a party this might apply to scouting a battlefield, planning a scientific endeavour or prepping your equipment before a dangerous hike. All things that done well might yield a bonus depending how well they were done, and in 2D20 it is baked into the rules and ready to go. In fact, it need not be difficulty 0 either. The GM can offer a roll with no real failure option to see how well they do. “This would normally be difficulty 0, but as you are outsiders at the party, I’m making it difficulty 2.” You might not get as much Momentum, but you can still ask around. By the same token the battlefield might be dark, the equipment substandard or the science something you are not familiar with.

Architects & Agents​

I should also add a special note for one thing we did with Dune, and that is architect and agent play. As Dune uses a Drive and Skill and not an attribute, the physical aspect of your character is not applied to the test. As such, using the same system, your character can fight a conflict from a distance using proxies (like a group of soldiers) rather than wade into the fight themselves. While it keeps them a lot safer, and perhaps protects their identity, if the plan goes wrong, it’s harder to improvise a response as you aren’t physically in the scene. What makes this a great piece of game design is that not only is it possible in the 2D20 system, but it also doesn’t require any rules changes. You use the same rules system no matter what approach you take, the only difference being how the scene plays out and what you options are afterwards.

So, whichever version of 2D20 you try, I recommend it’s worth a look. There are plenty of other good things about it, but its simplicity, momentum and difficulty 0 tests are my favourite aspects of the design. It has worked well for a wide variety of games and adapted to fit each one seamlessly, be it for Barbarians, Federation Captains or Sandworms.
 
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Andrew Peregrine

Andrew Peregrine



Puddles

Explorer
Thanks for the write-up, it does seem like a fun system with the momentum points, and I can certainly see the use of the Difficulty 0 tests. In fact, in my next D&D game when a situation like that occurs, I might ask the player to make 5 tests instead of the 1 I would usually call for and have the successes create a similar pool they can draw from.

A personal bugbear of mine is roll-low systems. From the read through there doesn't seem any inherent need for it to be roll-low and not roll-high so I imagine that comes from elsewhere in the mechanics of the game. :)
 


Ulfgeir

Hero
Thanks for the write-up, it does seem like a fun system with the momentum points, and I can certainly see the use of the Difficulty 0 tests. In fact, in my next D&D game when a situation like that occurs, I might ask the player to make 5 tests instead of the 1 I would usually call for and have the successes create a similar pool they can draw from.

A personal bugbear of mine is roll-low systems. From the read through there doesn't seem any inherent need for it to be roll-low and not roll-high so I imagine that comes from elsewhere in the mechanics of the game. :)
I think it is that in this case it is easier.

For roll low: add the two values (attribute + skill or relevant stats in the current game). That sum is the value you need to roll equal to or below.
For roll High, you would then have to also subtract that value from 20 to get the value to roll above..
 

Puddles

Explorer
I think it is that in this case it is easier.

For roll low: add the two values (attribute + skill or relevant stats in the current game). That sum is the value you need to roll equal to or below.
For roll High, you would then have to also subtract that value from 20 to get the value to roll above..
Yes, I see now. For roll-high in this situation you would require both a target number to beat and a target number of successes to reach. And that is arguably clunky, whereas in this case any roll under your stats is a success, no need for a target number, and the amount of successes required sets the difficulty for the task.

The Alien RPG has a dice pool and a target number, but you don't need x number of successes, instead you need only 1 and any additional successes allow you to perform stunts and other tricks.
 

eyeheartawk

Works 60% of the time, every time
The flexibility only goes so far though. Like, at the end of the day every game has metacurrency fueled dice pools that can be communally spent/used by the GM. I would argue most of these games, at the end of the day, function very similarly (This game uses these two integers to come up with a base TN while in this other game it's these other two integers with different names etc) with small tweaks to adjust the "feel". Fundamentally, I don't see the difference as any more significant than the difference between Dark Heresy and Only War or the difference between CoC 7E and Delta Green. Broadly, they all play interchangeably the same with more minor changes being made to adjust that feel. Ultimately, the fact that the system was built to be slightly more flexible at its genesis than most house systems doesn't obviate the criticism leveled against it that applies to most other house systems somehow.
 

Zaukrie

New Publisher
Interesting stuff, thanks!

One idea I have in my ridiculously long alternative initiative system document is similar to momentum..... Good to know I'm not insane. Probably.
 

Corone

Adventurer
A personal bugbear of mine is roll-low systems. From the read through there doesn't seem any inherent need for it to be roll-low and not roll-high so I imagine that comes from elsewhere in the mechanics of the game. :)
Its a 'your mileage may vary'. The maths is rather tricky to navigate though.
If you go the other way you are looking at a system where you want low attributes you can roll over, which doesn't feel right either.
The usual way past this is to base the target number just on the difficulty of the action, rather than the skill, but then you have to allow skills to modify the roll in some way or whats the point of them. But that means you start dealing in absolutes. If you add +5 for skill and an easy roll just needs to beat a 6 that character can't ever fail an easy roll. Make the bonuses too low and the advanced characters can't hit the higher difficulties. So it depends whats acceptable for success in terms of how heroic the characters are in the system that defines which way you go.
To be fair, D&D does this rather well, with attributes granting a bonus that isn't too unbalancing - but then you also get skill/proficiency bonuses leading to the problem above.
Its a maze designers have been navigating for years. Each setting usually demands different compromises, making it something that isn't usually too much of a problem. But its hard to it work for any setting.

I'm just glad my F**k/Yeah dice works either way. :)
 

Puddles

Explorer
Its a 'your mileage may vary'. The maths is rather tricky to navigate though.
If you go the other way you are looking at a system where you want low attributes you can roll over, which doesn't feel right either.
The usual way past this is to base the target number just on the difficulty of the action, rather than the skill, but then you have to allow skills to modify the roll in some way or whats the point of them. But that means you start dealing in absolutes. If you add +5 for skill and an easy roll just needs to beat a 6 that character can't ever fail an easy roll. Make the bonuses too low and the advanced characters can't hit the higher difficulties. So it depends whats acceptable for success in terms of how heroic the characters are in the system that defines which way you go.
To be fair, D&D does this rather well, with attributes granting a bonus that isn't too unbalancing - but then you also get skill/proficiency bonuses leading to the problem above.
Its a maze designers have been navigating for years. Each setting usually demands different compromises, making it something that isn't usually too much of a problem. But its hard to it work for any setting.

I'm just glad my F**k/Yeah dice works either way. :)

Yes, I am a fan of rolling high = good and high stats = good, which usually means a fixed target number with stats either modifying the roll positively or adding more dice to the dice pool. It’s just a personal preference and I like exploring the roll low systems too like the one outlined in this thread, but at the back of my mind I am always trying to figure out how I would change it to a roll-high system!
 

steeldrac

Explorer
Yes, I am a fan of rolling high = good and high stats = good, which usually means a fixed target number with stats either modifying the roll positively or adding more dice to the dice pool. It’s just a personal preference and I like exploring the roll low systems too like the one outlined in this thread, but at the back of my mind I am always trying to figure out how I would change it to a roll-high system!
you can always use the two skills as additive bonuses with a fixed TN of 20
 

pming

Legend
Hiya!

Not a system for me...particularily the "Difficulty 0" that seems to be that a Player gets to just "make shitaki mushroom sandwiches" and hand them to the DM to eat. The...:
“I’m buying an extra dice as I heard some gossip about this guy I’ll use when I challenge him.”
That sort of "built in system for the Players" just rubs me the wrong way for my gaming style. Don't get me wrong, I have ZERO problem with a system that has something like this...but it shouldn't be based on any sort of "dice roll" or "difficulty 0" type mechanic. The reason is simple; it pushes the DM to limit PC 'control' in an, imho, sort of underhanded way. I mean, if I don't want the PC's to completely destroy an NPC's "secret" on a whim...I'll just not tell them to make any Difficulty 0 checks. This is, effectively, the DM saying "naaa...not gonna let you for...reasons".

NOW, before everyone flies off the handle, as I said I'm NOT opposed to the concept. I just like to see it as a more "absolute, out of my hands completely" affair. Sounds contradictory, huh? But let me explain: With a Difficulty 0 method, I'm CHOOSING to let the players make it or not. I am the one in control of their narrative choice...but it also makes me feel like I'm 'cheating' if I don't allow a Diff-0 check/roll. The Players are under the illusion of being able to 'influence the story'. ... ... For me, an "absolute" system is better. One that outright gives players "4 Fate Points" that they can use at any time to ignore an dice roll or substitute a choice for a roll, or a system that gives the players "Drama Cards" (Masterbook has this; "Plot Deck"...taken from TORG, more or less, iirc). A player gets a set amount at the beginning of the game. If they don't use them, they can get "XP" (at least in my game) at the end of the session, or keep them. Or they can use them anytime they want during the session. I have no say in it. They use it whenever and I figure out a way to implement it into the story/combat/situation.

That I like! A lot! :) I don't WANT to be ultimately "in control" of if a Player gets to 'gain story points'. To tempting to, ahem, 'game the system' to control the Players choices. I still remember once playing Star Frontiers and using the Masterbook cards and plot cards; during a fight with gangsters in an industrial part of a big city on Morgaine's World. The PC's were...not doing wall and bad guy reinforcements were on the way...and a player who LOVES combat whipped out a Plot Card! (unusual for him). What was it? Well, a "PC's family member shows up", basically. O_O I had his sister show up as one of the gang member reinforcements. 😈 He loved it! It made for a sudden change of game play...the PC's suddenly were now wondering what to do....why was she here? How did she get here?

That, all because I, as GM had NO SAY in if a Player could/couldn't do something.

Anyway, that's my 2¢.

^_^

Paul L. Ming
 

Corone

Adventurer
Not a system for me...particularily the "Difficulty 0" t
LOL, your middle point is ironically one of my most loathed rules :) For me, I detest the 'unspent story points become your XP' as it penalizes players for using points to make a more interesting story, or makes them hoard them so they don't lose out in advancement. Hate it with a fiery passion. Although its not the use of story points as linking it to XP I really loathe.

I should add in defense of D0 rolls, it is up to the GM to decide if one is allowed. They can, as always, tell players any narrative they add while spending them isn't appropriate. Personally, I really like players having the option to expand and interact with the story in small ways. They might not have seen a weakness in a character, they might instead just know a good way to approach them politely, which grants the bonus without changing any of the story. Its very much a YMMV in style though. The main use is just to cover that 'I have a look around' action that PCs often do to scout a place out, when there is nothing specific they need to discover.
 

pming

Legend
Hiya!
LOL, your middle point is ironically one of my most loathed rules :) For me, I detest the 'unspent story points become your XP' as it penalizes players for using points to make a more interesting story, or makes them hoard them so they don't lose out in advancement. Hate it with a fiery passion. Although its not the use of story points as linking it to XP I really loathe.
Hhehe...yup. Different strokes and all that I guess, huh? :) That said, it's not much. It's just a little something (in D&D terms, it'd be like a 1st level character getting 25xp). Each Player gets two cards at the start of the session; either new ones or the same ones they had last session....wait, I didn't mention that did it? Sorry! (each card in the Plot Deck has a number specifically for this). So the Player can jot it down and save it for next session, or take the miniscule XP to get a different card for next session.

That way it doesn't "force" a Player to play a Plot Card they don't want to just to 'get it out of the way'.

I should add in defense of D0 rolls, it is up to the GM to decide if one is allowed.
Actually, that was kind of my point; that I don't like that because it then puts the GM in the position of "Ok, do I want the Players to be able to screw with the next part of the adventure they get to?"...if the GM is ambivalent, it's not a problem. But for GM's that like to "steer or guide" the PC's to some particular area/encounter/etc because that's what the GM has taken the time to prepare for the session, well...those GM's would have quite the temptation on their hand! ;) By "allowing" a D0 roll, that GM is basically saying "Yup, this next section could be done in 4 minutes in stead of 40 if a Player or Players use those 'extra dice to decide stuff'..."

They can, as always, tell players any narrative they add while spending them isn't appropriate.
But this was part of my contention: that the GM is almost encouraged to NOT allow D0 rolls specifically so he/she doesn't have to step in when a Player says "I'm going to buy dice to....because of...". Also, when a GM does this, it does give away info to the players...perhaps more than expected. Ex: "I'm buying dice to make a better Discern Truth roll. A guy at the Mos Eisley cantina was talking about seeing more Empire Stormtroopers than normal arriving...". If the GM rolls with it, he may have just given away what was supposed to be a surprising and exciting space chase or that at least one Star Destroyer is in orbit now...and if the GM steps in, then that just confirms that there is, indeed, a Star Destroyer in orbit or that SOMETHING is going on.

Not the greatest example, but I hope you get the point. "I'll use a point and say I know how this lock works completely so I can see if it's been tampered with": "Ok, yes it has" (Result: It's trapped), "No, I'm not going to let that happen" (Result: It's trapped). ;)

Personally, I really like players having the option to expand and interact with the story in small ways. They might not have seen a weakness in a character, they might instead just know a good way to approach them politely, which grants the bonus without changing any of the story. Its very much a YMMV in style though. The main use is just to cover that 'I have a look around' action that PCs often do to scout a place out, when there is nothing specific they need to discover.
I'm all for this too...I just like for it to be COMPLETELY out of my hands as a GM. If a game is going to give Players direct control over the story/narrative/goings-on....then it needs to be in their hands 100%. If the GM can simply "step in" and change it, or if the GM has a way of "not allowing the Players to get the 'points' to do it in the first place", then the game isn't, in fact, giving the Players the ability to affect the narrative.

^_^

Paul L. Ming
 

Like, at the end of the day every game has metacurrency fueled dice pools that can be communally spent/used by the GM. I would argue most of these games, at the end of the day, function very similarly (This game uses these two integers to come up with a base TN while in this other game it's these other two integers with different names etc) with small tweaks to adjust the "feel". Fundamentally, I don't see the difference as any more significant than the difference between Dark Heresy and Only War or the difference between CoC 7E and Delta Green. Broadly, they all play interchangeably the same with more minor changes being made to adjust that feel. Ultimately, the fact that the system was built to be slightly more flexible at its genesis than most house systems doesn't obviate the criticism leveled against it that applies to most other house systems somehow.
Momentum isn't shared in JCoM; it's individual.

The level of differences is sufficient to be problematic if playing two different ones at the same time in different groups.

  • Mutant Chronicles
    • Group momentum Pool
    • 8 atts, fairly traditional
    • 29+ skills (I'm working from the QS, as I don't have the core to hand)
    • Focus Value seems to be bought separately from the linked skill's level.
    • uses effect dice (called "Dark Symmetry Dice")
    • Two damage tracks (physical & "dread")
    • Metas: Momentum, Dark Symmetry, Chronicle Points
    • Extra d20s cost: flat
  • Conan
    • GRoup momentum pool
    • 7 Atts, fairly traditional
    • 25 skills, fairly traditional
    • Focus value generated equal to skill expertise (skill level), but independent after.
    • Uses effect dice ("Combat Dice")
    • Two damage tracks
    • Metas: Momentum, Doom, Fortune
    • Extra d20s cost: flat
  • STA
    • group momentum pool
    • 6 atts, not traditional ones, either.
    • 6 disciplines (super wide skills)
    • Focus value is either 1 or the discipline, depending on if the player has a relevant focus.
    • uses effect dice
    • one damage track
    • Metas: Momentum, Threat, Determination
    • Extra d20s cost: increasing
  • JCOM
    • Individual Momentum Pools
    • 6 Attributes
    • 0 skills
    • Focus Value lower attribute used in roll.
    • Uses Effect Dice ("combat dice")
    • 3 damage tracks
    • Metas: Momentum, Threat, Luck
    • Extra d20s cost: flat
  • Dune
    • Group momentum
    • 5 "Drives" (attributes)
      • high drives have "drive statements" - if the action doesn't jibe with the statement, you cannot use that belief.
    • 5 skills (super broad)
      • Skills may have focuses
    • Focus value is 1 or (if a focus of the skill applies), the skill level
    • No effect dice
    • 1 damage track (Stress)
    • Metas: Momentum, Threat, Determination
    • Extra d20s cost: increasing.
By flat, I mean: 1st extra costs 1, second extra costs another 1 (for 2 total) and the final costs 1 (for 3 total)
And increasing: 1st extra costs 1, second costs 2 more (for 3 total), and final costs 3 (for 6 total)
This difference has tripped up players. (Especially since early playtest for STA was flat)

There are a few flaws with the core system that stand out:
  1. injudicious use of increased threat range (or really bad luck) can create situations where player success is clearly due to GM's pulling punches - as indicated by a stack of threat unspent at end of adventure. (I've had "Doomed to Repeat the Past" end with 20+ threat in the threat pool 3 times. The initial playtest adventure I had one session with snowball - and that ended with over 20 as well. Players were sorely demoralized by this.)
  2. since there's no mechanical benefit to the player, nat 20's being unannounced by the player have been an issue with a less than scrupulous player. (I've seen this in two different occasions and a total of 3 players.)
  3. the difficulty labels only seem to fit if no momentum is used.
  4. roll low.

Of these, only #1 is a significant issue. Dune reduces the impact of snowballing by limiting threat spends, so a session ending with a pile of 20 threat isn't "Damn, he took it easy on us!"

#2 is fundamentally a player honesty issue, but one that, for example, Cortex Plus solves by making the bad number pay the player when the GM uses it, rather than charging the player to ignore it.

#4 is really a matter of preferences, since the math can be coerced to work either way... but, even by grade 4, IME, Alaskan kids have a significant (2/3) preference for roll high. (I asked a bunch of kids while subbing.)
 

Corone

Adventurer
The flexibility only goes so far though. Like, at the end of the day every game has metacurrency fueled dice pools that can be communally spent/used by the GM.
I should be clearer that I'm not suggesting 2D20 is special for having beanie points. They are pretty commonplace in any rpg.
What is rare that 2D20 does is make them much easier to acquire and quicker to spend as they are not a random GM award but a commonplace bonus.
The difficulty 0 roll is great not specifically for handing out points, but for making an often tricky player action simpler. Usually the PCs having a general scout around leaves the GM trying to figure out something useful to give them, or just struggling and saying there isn't anything special. But the difficulty 0 roll gives bonus points rather than offers a specific detail or success/fail result. So those points and the advantage they offer grants a tangible advantage the players can use for scouting out ahead without facing the GM to list every detail and then see if it becomes useful. On top of that you can add whatever narrative you like.
 

I should be clearer that I'm not suggesting 2D20 is special for having beanie points. They are pretty commonplace in any rpg.
What is rare that 2D20 does is make them much easier to acquire and quicker to spend as they are not a random GM award but a commonplace bonus.
Fate in Fate is used only slightly less frequent than 2d20. In my limited experience with Fate, well over 80% of rolls had fate spends.

2d20, metacurrency use is (at least in Dune and STA) one or more used in above 95% of rolls. Spend decisions are relevant in abut 99%.

Cortex Plus/Prime is harder to figure; given an fairly typical roll of 1d10 +2d8 +1d6, that's 1-(0.9×0.875×0.875×0.8333), or about 42% of rolls generate 1 or more complications. That's just the generation side of things, and not the only method, either. my estimation is about 99% of rolls involve a spend decision (do I or don't I?).

FFG-StarWars/Genesys has one metacurrency as well, but it's used between 5% and 20%, varying by playstyle and GM willingness to spend on NPCs.

Of the big 4, only 2d20 doesn't reward you for pushing your bad rolls forward to the GM's attention. It's a minor thing, and it's not a lot of players, but I've had 4 players who would, and 2 more who did, conceal their 20's in my play. One of whom wasn't in a one-shot at the local con.

What I edited to add: I like the way it plays generally - the snowball effect isn't an all the time thing; I don't mind the three metacurrencies...
but the different names for the same metacurrencies is a place for confusion.
 
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