Have you ever fumbled with a flail? It sucks, especially when you are first learning it. It can happen very often; Sometimes in such a terrible way it far surpasses the risk of swinging a staff, hands down.

I'm interested in trying/viewing/hearing about a system that has variable critical miss chances. While I'm familiar with the d20's five percent critical miss chance and the five or greater percent critical hit chance, I've seen expanded chances of neither critically missing nor terrible things happening. Not even a greater chance for characters with nunchukus to hit themselves than characters wielding less-potentially-lethal-to-the-wielder weapons.

Moreso, I'm interested in any games that model this using percentile dice. 2/20 would seem a large jump from 1/20, but 7/100 wouldn't be as bad raised from 5/100.

If there is a system that models this...

  • How is the critical miss range determined?
    • Varying levels of weapon/skill proficiency?
    • Did it vary with the weapon used?
    • Class/path/character's set role?
  • What is your (experienced, preferably) assessment of it's impact on game play?
  • \$\begingroup\$ Related: rpg.stackexchange.com/q/2/4089 and rpg.stackexchange.com/q/7490/4089 \$\endgroup\$
    – LitheOhm
    May 21, 2013 at 3:45
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    \$\begingroup\$ Pretty sure that no one who has even a 1% chance of hurting themselves with their own weapon every time they swing it has any business on a battlefield, wielding that weapon. So I'd suggest looking for systems that model characters that have little training and find themselves forced to defend themselves with weapons they are not familiar with. A system that focuses on trained warriors using weapons they know well would need to have extremely fine granularity to model something like this. \$\endgroup\$
    – KRyan
    May 21, 2013 at 6:15
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    \$\begingroup\$ GURPS does a good job of criticals dependent on skill, where skill can be modified by everything from weapon to weather conditions. Would you like, I can show you how to represent this in d100. \$\endgroup\$
    – illotum
    May 21, 2013 at 6:59
  • \$\begingroup\$ @KRyan perhaps. I can't refute that at the moment, but I imagine even 1/100 isn't horrible odds for some weapons. \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 17:41
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    \$\begingroup\$ Sounds like you have an answer, @illotum . Please post it! \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 22:17

6 Answers 6


Rolemaster (Standard and Classic) uses a variable fumble chance for every weapon.

Critical Miss Chance

Rolemaster uses a cascading d% system (01-05 roll down 96-00 roll up) but unmodified rolls within the weapon fumble range automatically cause a fumble (and a roll on the appropriate weapon fumble table)

Varying by weapons

Sample weapon fumble ranges:

Morning star and flail 1-8
Hand axe 1-4
Mace 1-2
Dagger 1

Additionally some weapons inflict criticals on the wielder if they fumble - these tend to be the more exotic weapons however, like the Ge (a kind of super bola) causes a unbalancing crit if a fumble is rolled.

Finally there is a Weapon Expertise skill (in Rolemaster Companion 4 - Classic system) that can be bought to lower the fumble range of a specific weapon. (By one % per rank in the skill bought to a minimum of 01)

Class/Profession set role

As far as classes (proffessions in Rolemaster) are concerned there are absolutely no restrictions as to who can use what type of weapon, the skill cost for weapons simply increases. In Rolemaster weapons are in categories (one handed edged, one handed blunt, two handed, bows, thrown) and costs are assigned at character generation for each category. Weapon skills are, however, bought per weapon at these category costs.

Professions like fighters get very low costs to choose and split between weapon categories, professions like mages get one high-ish cost for a category and very very high costs for every other category. So a mage can quite happily wield a two handed sword, they'll just not be very good at it.

Game experience

As to experience of weapon use/fumble range in play, players tended to view flails and morning stars as extremely dangerous (due to the high fumble range but I also used an optional rule from one of the companions that meant fumbling a flail inflicted a crit on the wielder)
However the bonus for using these weapons was that they were much more damaging and any enemy they encountered using these got a "whoa nutter" sort of reaction as well as a much higher threat perception from the players.

Experienced high level fighting characters liked to reduce their fumble range for weapons down to 01-05 at least (if higher than this) so 01-05 was a fumble, everything else was a potential hit. One extremely weapon focused berserker character used a morning star and a Falchion (two weapon combo) and had reduced both fumble ranges to 01, he also only ever used the morning star when in a berserk rage which reduced criticals taken by himself so any fumble with the morning star didn't actually hurt him.

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    \$\begingroup\$ Sounds like your players were properly respectful of the dangers of wielding flail-type weapons, and conscious of needing to train up to use them safe(r)ly. That sounds ideal! Big +1 for detailed personal experience. \$\endgroup\$ May 22, 2013 at 15:20
  • \$\begingroup\$ Very nice :) this sounds extremely close to something I'm working on - I'll definitely have to try it out. +1! \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 17:44

There was an old system called Rolemaster that did this sort of thing. It was published by a company called 'Iron Crown Enterprises'. I'm not sure if it's still in print, but you could probably find copies of it on ebay. This had quite an elaborate system for dealing with weapon fumbles and critical hits.

Try searching for 'Character Law', 'Arms Law', 'Spell Law', 'Creatures and Treasures' and 'Rolemaster Companion'. According to the Wikipedia page there were also revised editions published later. The publisher also licenced IPR from Tolkien's estate and published a simplified version called Middle Earth Role Playing (also known as M.E.R.P.). They also published dozens of adventure modules in that setting, so you might have a bit of fun with retro gaming if you're into that sort of thing.

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    \$\begingroup\$ Doh! Answered at the same time, should have sent mine before breakfast instead of after ;) \$\endgroup\$
    – Rob
    May 22, 2013 at 8:27

In Legend and RuneQuest 6, your critical chance is 1/10 of your combat skill, rounded up. As RuneQuest 6/Legend is a percentile system, it's quite easy to calculate the percentage - if you have a combat skill of 50%, your chance of a critical is 5% (roll below 5 on a d100).

Fumbles is only 2% - on a roll of 99 and 100. However, RuneQuest 6 has an 'advantage' mechanic in which different degrees of success allows the victor (who could be the attacker or defender) to spend on various manuevers, such as disarms, called shots and such. For instance, if the attacker manages to roll under his combat skill while the defender fails to, he gets 1 Success. if the attacker rolls a critical and the defender fails to roll under his combat skill, the attacker gets 2 successes. This, in a sense, simulate varying degrees of fumbles/critical.

Dungeon Crawl Classics introduces another critical table when you score a critical hit. The table rolled on depends on your class; the number you rolled is modified by your level and other stuff.

  • \$\begingroup\$ Interested in what 'other stuff' affects it in Dungeon Crawl Classics. I don't understand the "success" mechanic? I do like Legend's and RuneQuest 6's scaling critical hit but that's not what I'm after - is the 2% fumble static? \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 17:52

Spycraft 2.0 has error ranges.

To sum up, generally rolling a 1 (and failing, thus if your skill is high enough it may be avoided) results in an Error. An opponent may then spend an action die to convert it to a critical failure. But feats and talents can modify the error range both ways so you can end up having 0 chance of error as easily as 15%. You still have to be failing the check, and most of the time an action die still has to be spent to trigger it, though, so it doesn't always mean a Critical Failure.

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    \$\begingroup\$ Fantasy Craft (the fantasy brother of Spycraft) has the same error range mechanic. \$\endgroup\$
    – Granger44
    May 22, 2013 at 17:08
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    \$\begingroup\$ Interesting, opponents can affect it. I'm definitely for affecting the range through feats/talents etc. +1 \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 17:49

Let's deconstruct the problem first

You want a chance of really bad outcome to:

  1. scale with a skill level
  2. be conditions dependent: weapon type, visibility, whatnot
  3. be a flat percentile

Rob made a great Rolemaster overview, so I'll concentrate on Unknown Armies. Game satisfies all three conditions and is quite easy to explain.

Unknown Armies

  1. Uses a cherry system where something exceptional happens when you roll a double. Lower than skill means success, higher than skill means failure, with cherries happening, basically, one in ten rolls. (Character also has an obsession skill with which )
  2. Skill is modified situationally by GM discretion up to +/- 30 which also modifies a critical chance.
  3. It is a d100 with the average skill of 30.

To your additional questions:

  • No, weapon modifies damage only.
  • Closest resemblance to class system is an obsession skill. Player can optionally swap the digits in the result of obsession skill roll to get a success -- obviously you can't swap a cherry.
  • In our games, cherries weren't intrusive or overwhelming. But it is inexplicably more fun to look for doubles instead of number comparisons. Keeping in mind average skill of 30 (and conditional penalty up to -30) in this system you can stumble and break your neck quite easily.

GURPS variation (advanced hacking)

Original mechanic is dead simple:

  • 3 is always a critical success, 18 is always a critical failure
  • in addition, any result that is lower then skill - 9 is a critical success, and any result higher than skill + 9 is a critical failure.

But it is impossible to implement in flat d100 without using complex math. Why? GURPS roll (3d6) has a bell-curve probability distribution opposed to a flat d100 Starting chances are very small, but they grow exponentially.

For the sake of simplicity we'll go with the linear progression

  1. To get a critical you need to roll a number of full tens higher/lower than your skill level.
  2. Every weapon gets a critical rating of how many full tens you need to get a critical. If you want it to be asymmetrical, rating needs to be two numbers -- for success and failure.

For a weapon with crit rating of 3 / 4 and skill 40, you has:

  • crit success for rolls of 1..10 (40 - 3*10)
  • success for rolls of 11..40
  • failure for rolls of 41..80
  • and crit failure for rolls of 81..00 (40 + 4*10)

That's a solid foundation which you can build atop. By coincidence it is very similar to the system used in Warhammer 40k books by FFG. You can read them for a full blown example, with weapon tables and all.


In "Drakar & Demoner" (in the Gigant expansion, definitely), using a D20, there's a risk of fumble on rolling a natural 20. To actually fumble, roll for skill again and fail. This means that at skill 1 (approximately "worse than untrained"), you have very close to 5% of fumble, but at skill 15 (approximately "master and beyond"), you only have 1.25% chance of fumbling. Even if your skill managed to get over 20, rolling 20 for the skill check warrants a second roll and 20 again means fumble (so no matter how goot you are, you have 1/400 of fumbling).

In the precursor system (percentile-based), ISTR that you fumbled on 96-00 is your skill was 20% or below, 97-00 from 21%-40% and so on, with 00 always being a failure (and fumble, I think).

On the success side (D20-based rules), you succeeded on rolling equal or under your skill. On a 1, roll under skill again for a critical hit (full weapons damage, no armor protection). On 2-5, you roll again for a "special success" (semi-crit, full weapons damage, armor still counts). A successful parry of "same level" is still a parry.

For skills in the range 20-39, 1 is an automatic crit, 2 is a potential crit (roll skill-20 or lower, fail means semi-crit), 3-5 are semi-crit and 6 is potentially semi-crit (roll skill-20 or lower). At least IIRC (I am actually not sure if 3-5 were auto-semi-crits or handlked the same way as 6 and I don't have the rules at hand).

The following paragraphs are my recollections, but they may well be recollections of house rules, not RAW.

IIRC, a parry of one level lower (that is, successful parry against semi-crit attack counts as only normal attack; semi-crit parry against a crit attack counts as a semi-crit attack).

A parry that is one (or more) level(s) "higher" (crit parry against normal/semi-crit attack; or a semi-crit parry against a normal attack) disarms the opponent.

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    \$\begingroup\$ +1: a system that gets the granularity the OP is looking for, that demonstrates that there are more ways to get it than using specifically percentile dice. \$\endgroup\$ May 22, 2013 at 15:17
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    \$\begingroup\$ @SevenSidedDie: There were also an assortment of crit/semi-crit successes. Might actually be worth my while editing my answer to get those in, as well. \$\endgroup\$
    – Vatine
    May 22, 2013 at 15:45
  • \$\begingroup\$ @Vatine I'm certainly interested. Weapon skill calibrating it instead of just percentile dice is what I have in mind, too. +1 \$\endgroup\$
    – LitheOhm
    May 22, 2013 at 17:47

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