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Musings on the Target Number

Life is like a bag of d20s

I have an occasional tendency to second-guess whether Chimera handles such-and-such as well as I’d like (some of you are already familiar with this irritating habit of mine, by virtue of having seen what amounts to 3 major and 10 minor revisions of Chimera since 2006). Last week, Target Numbers were in the crosshairs, and I thought I’d retrace my thought process for input.

Initial Thoughts

The basis for Chimera Action Rolls is that you toss a d20 every time your character does something meaningful. If the result is equal to or greater than the required Target Number (TN), the attempt succeeds.

20-sided die

My Fav d20

Simple enough, yet this elegance disguises a few “attractive nuisances” for a tinkerer like me.  Chief among which is how you assign difficulty. There are two ways to do this:

  • Adjusting the TN: the higher the TN, the harder the action.
  • Modifying the roll: positive modifiers make the action easier, while negatives make it harder

The pitfall (for me) is whether to use one method or the other, or a combination of both.

Static Target Numbers

I experimented with static TNs (i.e., a roll of X or better always succeeds, no matter what you’re doing). If you go this route, the TN is always the same so you have to reflect difficulty by modifying the actual roll.

Chimera 2.x had a modified version of this: your TN in a given action was based on how you assigned the attribute you were using. Actions performed using your Primary Attribute were TN 8, actions using your Secondary Attribute were TN 12, and actions using your Tertiary Attribute were TN 16.

This had the nice benefit of giving different characters different TNs for the same action. Success was always based on what the character brought to the table—a PC with Strength as his Primary could bash down a door with TN 8, while another PC with Strength as his Secondary would bash the same door at TN 12.

It also made it easy to determine the required TN for a given roll. No subjective dithering about whether an action was “Hard” or “Very Hard.” Oh, you’re trying to find a clue and Intelligence is a Tertiary Attribute? Roll 16 or better.

Now, despite what I wrote a few paragraphs ago, the GM could still adjust the TN to reflect difficulty, but such adjustments were done in increments of TN +/-4. And that could get onerous, especially when skill improvements were applied in increments of +/-1. Good on paper, but not always fun for the players.

Action Roll Modifiers

Chimera 3.0 (aka Chimera Basic) got rid of this convention wholesale by ditching attributes and moving entirely to Abilities. In this model, class-based Abilities start at TN 16, and each improvement reduces that by 1 (i.e., a class-based Ability that you’ve improved 3 times is TN 13).

It’s simple, but not intuitive. First, where did 16 come from? Second, doesn’t it make more sense for an improvement to be “+1” instead of “-1”?

Well, the first bit hails from my B/X days, when I revamped action resolution in my Classic D&D game. Unfortunately, a D&D 16 is easier to attain than a Chimera 16, so that didn’t quite work as well as expected. The second bit—using “-1” instead of “+1”—is just pure idiocy on my part. Of course “plus” means better than “minus.”

Another aspect of this approach was that I started tweaking Action Rolls from both sides, meaning the Chimera Basic rules are rife with situations where you adjust the TN, but there are also plenty of times when you adjust the actual d20 roll.

In practical terms this means that an adjustment of TN +2 (i.e., making the required TN 2 points harder to achieve) is the same as AR -2 (i.e., subtracting 2 points of the roll result). In other words, if I’m up against TN 16, an adjustment of TN +2 or an AR -2 both actually mean that I need to roll an 18.

I find this partially confusing, because it erodes the consistency of assigning difficulty to an action. Do you tweak the TN or the AR modifier? Does a low-visibility penalty reflect the action’s inherent difficulty or just how poorly your character deals with dim light?

And, while this system allowed you to easily record each action’s TN (e.g., “Wield/14” leaves very little room for ambiguity), the benefit is offset by the potential inconsistency with which the action’s difficulty is affected by external factors.

Logical Blend

My OCD leads me to the following approach:

  • The GM assigns Target Numbers based on an action’s inherent difficulty (see below)
  • The PC modifies his Action Roll based on external factors (skill, environmental conditions, special gear, magic, etc.)
  • Abilities are recorded with their AR modifier (e.g., “Wield +2”)
  • Resistance rolls and other actions are recorded with their actual TN (not a TN or AR modifier)

Based on difficulty, the Target Number scale looks something like this:

  • Automatic: TN 2
  • Very Easy: TN 4
  • Easy: TN 8
  • Average: TN 12
  • Hard: TN 16
  • Very Hard: TN 20
  • Impossible: TN 24

Similar to what Chimera 2.x presented (and reinforced by Deimos, whose wisdom is great).

But what about smackin’ the beasties? I think the TN is based on the target’s size. I’ve wrestled with Size-based “to-hit” modifiers before, but couldn’t make them work without extra bookkeeping. But this may be the “right” way to introduce this aspect of fighting. What about:

  • Target is smaller than attacker: TN 16
  • Target is same size as attacker: TN 12
  • Target is larger than attacker: TN 8

The only “hitch” to this system is that I think it’s pretty much what d20 or D&D 3.x already uses. That’s not necessarily bad (meaning, if it’s more familiar to players, then it eases Chimera’s learning curve), but I’m not versed enough in 3.x to know where the disadvantages lie.

Final Words

OK, the skeptical amongst you will count this as minor revision #11. But (and I stress this), the approach above doesn’t alter how Chimera Basic is played—it merely changes how the Action Roll/Target Number rules are presented. You can use your characters and stat blocks as they exist now—just subtract current Ability TNs from 16 to figure the Action Roll modifier (e.g., Fight/15 = Fight +1).

That said, I plan to roll this around for a few days and actually write it out. If it passes muster (and pending your feedback), this will make it into the 5th (and I think final) printing of Chimera Basic.


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  1. February 16th, 2011 at 13:32 | #1

    Firstly, there are two basic ways to handle checks, and in the history of Chimera RPG, you have used both of them. I mentioned both of them in my comments and discussions on my forum, and I will reiterate them here.

    The first is a task-based approach where the difficulty is actually determined by the task and the character themselves. Chimera RPG uses this when it has things like “Wield/16″ – the standard TN to use the Wield skill is based from the character themselves, and the task they are doing. Other systems that have used this include Warhammer Fantasy Roleplay, for example, which is a percentile based system. It generally provides a flat chance, with modifiers based on circumstances.

    The second is a conflict-based system, where the difficulty is actually determined by something that the character is in opposition with. These are generally roll highest systems, and is the system that d20 uses. Yes, D20 uses flat DCs, but it is worth noticing that in all cases, these DCs are based on the assumption that the opponent is taking 10 – useful if they are not actively opposing the character making the check. Meanwhile, the character themselves provides modifiers to make their checks better or worse as do circumstances, but it can be tricky to detemine whether a circumstance is a bonus for the character, or a penalty to the opponent.

    With this in mind, as easy as it may seem to switch Fight/15 to Fight +1, this is actually a switch in how check resolution is interpreted, and a lot of the confusion in Chimera that you describe comes down to not understanding and/or not sticking to a task-based or conflict-based system and knowing the limitations of benefits of each type of system.

    What you intend to do for minor revision #11 is, in fact, switch from task-based to conflict-based resolution. Although you make it look like you’ve got set TNs for opposition, it’s still a conflict based system, but you’ve already assumed that the default result for an average check will be 12 – based on the “average” difficult and attacking a “same-sized” attacker respectively. From this, it’s easy to see that each step of difficulty provides a +/-4 modifier to the opposing roll, resulting in the TNs that are given – it’s easy to equate that smaller and larger are single steps of difficulty, and make it easier to combine these modifiers with other rolls.

    You are right – it IS pretty much what d20/3.x uses – except that instead of a base of 12, it assumes a base of 10, and instead of +/-4 per difficulty step, it assumes +/-5 (although a standard circumstance modifier is in fact +/-2, so miscellaneous modifiers rarely balance the standard printed ones).

    In general, you are looking at the advantages vs. disadvantages of task-based and conflict-based systems. Generally, task-based systems are easier to learn, but much more limited, and have difficulties handling multiple opponents in the same check. They are fine if you just want a flat number to roll and don’t want a lot of modifiers, a lot of fuss, and a lot of rules, and make them best for more narrative-based systems.

    On the other hand, despite their familiarity, especially thanks to the d20 system, conflict-based systems are better for more complex and simulationist approaches. They are often initially a bit more complex, particularly if they require more die rolling, but the flexibility they provide, particularly when handing more complex scenarios more than make up for this. With a conflict-system, the same approach that the GM can use to define set TNs from rolls for opponents checks can easily be reverse engineered to allow the players to make more or less rolls to change gameplay as needed.

    For example, D20’s AC/Defence is basically 10 + modifiers, so the 10 can easily be replaced with a d20 roll, and now you’ve got players rolling for defence – which may be useful for allowing a more video game feel, or for simply putting the control of the dice in the players hands – one of 4th Edition’s better improvements involves changing how certain spells work, so rather than reflex saving throws to avoid an automatic spell, it becomes an attack roll to have the spell affect the target. All this, simply by swapping which d20 was rolled and which were assumed to be “taking 10.”

  2. February 16th, 2011 at 14:05 | #2

    UPDATE – I forgot to mention that another aspect of the “blended” approach is that PCs don’t necessarily know the TN they’re shooting for. In my experience, some GMs prefer this, others aren’t as strict, so YMMV.

    @Da’ Vane : As foreign as terms like “task-based” and “conflict-based” are, I’m seeing the difference, and yes, it appears that Chimera has used both. Also, you’re right–I’m assuming a base 12 in the logic that, all things being equal, an attempt has a roughly 50/50 chance of success (well, 45/55 in this case, but you get the idea).

    It may be that I’m giving the conflict-based approach more thought now that I’m writing the Core, and there are more complexities to consider. Opposed rolls is one example, and it’s essentially a highest result wins thing (though a Critical Success trumps a Normal Success). With the goal of achieving the easiest way to arbitrate actions, I’m finding that assigning TNs and AR modifiers consistently is the biggest factor in streamlining the system.

    task-based systems … have difficulties handling multiple opponents in the same check.

    Can you provide an example, please?

  3. February 17th, 2011 at 13:28 | #3

    I believe I already did when I was discussing how Initiative could be made into a check rather than a simple roll on the Initiative thread.

    Essentially, you would have to make an initiative check for each person requiring initiative, and then create a list based on their success. Using the way Chimera RPG currently works – you would basically have four steps in initiative. From fastest to slowest, these would be: Critical Success, Success, Failure, and Critical Failure. This is quite a complicated procedure for something that seems so simple.

    Initiative under a conflict-based system, however, would simply have all the characters roll high, and then act in order of their rolls from highest to lowest. Each character is considered to have beaten the TN of those that rolled lower, and failed to beat the TN of those that rolled higher. It is much simpler.

    With regards to Criticals in a conflict based system, these may need some tweaking, especially since the TN itself is largely defined by the opposition, and this is what is used to defined whether a critical is a success or a failure. After all, in a conflict-based system, the opponents are often rolling as much against the PCs as the PCs are against their opponents, so might suffer from luck as much as the PCs would. Of course, a thought shift might solve this very easily – rather than making criticals referential, simply have criticals – since a good result for the PCs is normally a bad result for their opponents, and visa versa. Thus, an opponent rolling a critical would handle bad luck for the PCs, without needing any messy referencing. This would also have the advantage that if the PCs opponent’s do not roll, they do no get any luck – so PCs are not going to be subject to bad luck when dealing with non-active opposition, such as scenery.

  4. Greg MacKenzie
    February 21st, 2011 at 08:10 | #4

    I applaud your efforts to improve your game, however, I think this is overcomplicating things. I’ll look at this from my ol’ schooled brainpan and you can let me know what you think. In my opinion all a Player and GM really need is a simple TN to achieve on a d20. The player needs to know what that is. Taking a look at this as a table your values go off the upper end of the d20 roll:

    A VE E A H VH I
    2 4 8 12 16 20 24

    I would scale this differently, removing the Impossible task, and I would also eliminate Automatic for reasons which I’ll explain later. The table of possible die rolls looks like this:

    S R D H X
    4 8 12 16 20

    S – simple, R – routine, D – Difficult, H – Hard, X – eXtaordinary

    There is a bit of perceptional difficulty with the table, in terms of psychology, where in the mind more is typically equated with better. In the case of the table more appears worse. In D&D for example the higher your character progressed the lower the hit number your character had to roll got. Perhaps the same table should be expressed thus since we are rolling the TN or higher:

    X H D R S
    20 16 12 8 4

    I think you need to identify when a shift of 4 points is required to move the TN from one column to the next. Modifiers to the die roll in increments of 1 pip only complicate matters. Combat between peers should occur without a shift. Combat between non peers, say between a Giant (L) and a Mansized Character (M) should cause a simple shift either left or right on the table.

    Man to Giant, the TN should be worse, i.e. Man v.s. Giant the TN should be 12 shifted to 16.

    Giant to Man, the TN should be better for the Giant, TN 12 shifted to 8.

    You could cite other reasons why you may want a shift, however I would lump the “causes” together allowing only one shift, you are moving 4 pips of the die.

    I would avoid the use of any modifications to the die roll beyond a half shift to the TN, i.e. +1 or +2 at the most. These should be due only to “character driven” ability modifications. That way the players can keep track of whether they get to add to their die roll. Note that I identify the shift as one way only since they have to roll the TN or better.

    I would avoid any minus to the die roll due to environmental conditions or other mitigating factors. In the long run these only serve to clutter up the game play.

    I would remove automatic hits and automatic misses, if you miss the die roll you missed. Only a prone, incapacitated opponent should be struck automatically.

    Criticals are useful but perhaps should be handled differently. Because they add an element of the chance of success to any un-equal situation it is a loophole. However is it truly useful?

    If you hit that is a NS – normal success, if you fail to hit, that is a NF, normal failure. If your TN was 12 and you roll >=16 or =20 on the die, that is a CS – critical success and additional benefits are indicated. Conversely if your TN was 12 and you roll an >=8 or >=4, these are CF – critical failures and a penalty is indicated. A problem kind of arises when a TN is 4, there is no possibility of a CF. Should that be allowed to stand? Perhaps that is why you extended the table on one end to 24. If you must have Criticals they need to be equal on both sides of the table, you would have to extend your table in the opposite direction to -4, you could go as far as 24 28 32, -4 -8 -12.

    In the end it may be that the model of calculating criticals CF/CS is over elaborate:

    Model 1 – all you really need is a die roll of 1 or 20, if you need them at all. Under a 1 or 20 mechanic, ignoring the machinations of trying to figure out what is a CF or CS by fours is averted. When a critical is indicated roll on a second table to determine what the result is.

    Model 2 – Should the critical be calculated as part of a TN die roll result? Perhaps it should apply to wounds suffered instead. As a part of that calculation. Let the dice fall where they may. :)


  5. February 21st, 2011 at 13:54 | #5

    Still drives me crazy that opponent skill has no impact on the difficulty to hit him in Chimera. Since Bruce Lee (assume he’s still alive for this example) and Stephen Hawking are both average-size humans, my character’s chance to hit either is identical.

    I understand that all RPG systems are an abstraction, esp. combat systems, but this is where my Suspension of Disbelief goes “SPROING!”

  6. February 21st, 2011 at 14:22 | #6

    @Greg MacKenzie : Good analysis. This sort of goes back to the Chimera 2.x model, which had 7 Target Numbers of ascending difficulty, and all modifiers shifted up or down the scale. For example, if you were attempting an Easy action (TN 8), but something made it harder, it shifted to Average (TN 12). I liked this approach because it made modifications very easy.

    However, it didn’t seem to take off, perhaps because it didn’t provide much granularity. Maybe it wasn’t well-presented. I do like your “number line” approach of your table–kind of a Target Number Slide Rule™…

    I’ll think on this a bit–as always, it’s the old ‘ease of playability’ thing.

    I believe I’m going to hold fast on the Criticals, as I like the idea that they could occur all along the d20, as it were (i.e., not just limited to the extremes; Hârnmaster did something similar with their percentile system).

    At a high level, making Criticals occur on a natural roll divisible by 4 means there’s a 25% chance of something extraordinary happening any time an Action Roll is made. If your TN is 12, for example, 3 times out of 5, that thing is extraordinarily beneficial (conversely, there’s a 2 in 5 chance that it’s extraordinarily bad).

    The extremes of the d20 do help out here. If your TN is 2 or less, a roll of 1 gives you a Critical Failure. If your TN is 21 or more, a 20 simply gives you a Normal Success.

    The other benefit of using Criticals this way is that it gives you 2 more outcomes on the Action Roll (i.e., more than just Normal Success or Failure), and these outcomes can occur more than 10% of the time.

    This might make more sense after seeing the upcoming draft, which will be ready shortly. Got to follow through on some other project work I promised… ;)

  7. February 21st, 2011 at 14:29 | #7

    @Rich Spainhour : This will change a bit in the next update. I’ve added Parry, which is added to the TN required to hit. Let’s say I hit a man-sized opponent on TN 12. If Bruce Lee had a Parry of +4 (let’s say), I now need a 16.

    Parry is reflected by shields, cover against direct attacks (i.e., any attack that isn’t area-of-effect), certain weapons, and certain Perks/Special Perks.

    Does that help recoil your suspension of disbelief?

  8. Greg MacKenzie
    February 21st, 2011 at 15:01 | #8

    Rich Spainhour :Still drives me crazy that opponent skill has no impact on the difficulty to hit him in Chimera. Since Bruce Lee (assume he’s still alive for this example) and Stephen Hawking are both average-size humans, my character’s chance to hit either is identical.
    I understand that all RPG systems are an abstraction, esp. combat systems, but this is where my Suspension of Disbelief goes “SPROING!”

    I had a thought with regard to this and the opposition of unequals is handled by the rules. By the basic rules if you were to re-create this fight between two unequal fodder characters, the weaker one should have a worse Ability to fight TN 20. Bruce Lee would be TN 14 or so, or better, depending on what you decide their abilities should be at the outset. While the game presumes that player characters are somewhat equal in their starting point, four points to specialize, the Fodder characters have no such restrictions to apply to them. You would sort them out based on what you wanted them to do. Of course if the wrastlin’ were done in quatum phyisics the fight might be completely reversed. So that’s my take on this. Greg

  9. February 21st, 2011 at 18:55 | #9

    As long as you don’t fall into the trap of Warhammer Fantasy Roleplay (1st or 2nd ed), which was also a task-based system: The way they worked is that they had skills like Parry and Dodge Blow that were actually checked, and if successful, completely negated a successful strike. This drastically slowed down combat, particularly if both were highly skilled, because you’d have situations where there would be a 90% chance to hit, and then a 90% chance to avoid the blow, round after round. This meant that there was actually just a 9% chance of striking your opponent…

    So, Erin, basically Parry is Defence/Armor Class… Sounds suspiciously like the Legend of Zelda Roleplaying Game there… Ahem… (Runs away!)

  10. February 25th, 2011 at 13:58 | #10

    @Erin D. Smale

    I’ll have to see the implementation, of course (and I’m really looking forward to the 5th printing), but that seems like what I’m looking for.

    It reminds me of the Parry mechanic in Savage Worlds, which works just fine for me at that game’s level of abstraction.

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