Open Ended D10

From RPGnet
Revision as of 16:03, 14 August 2006 by (talk)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

Here I present a game mechanics idea I have for a possible game system I might do some day in the future. Things never get done until you write them down, so I decided to include it here in the wiki. You're all of course invited to use it in your own games and tweak it as you like.

I just want to take the typical d100 roll you find in Runequest (with critical hit and miss) and the open ended d100 roll in Rolemaster (with an infinite array of results) and meld them into a d10 roll. I find d100 rolls a mess because rolling two dice at the same time usually means that they scatter all around the table and floor, and they make calculations (as including modifiers or determining success) more difficult without actually adding anything in return.

Enrique Martín, 2006.


I will begin this article with an example. The rules per se are explained in the following sections. Let's go :

Dorbud the thief is trying to sneak into a mansion and needs to silently pick a lock. The Game Master calls for a Lockpicking skill test, and Dorbud's score is 3 out of 8(he's not very good in this trade). So, Dorbud's player rolls 1d10 and...

  • Rolls a 3, success. ¡He makes it! After several minutes fumbling with his lockpicks, Dorbud opens the door and sneaks in.
  • Rolls a 8, failure. Dorbud spends some time working hard but to no avail. As he cannot risk staying in that place for much longer, he will have to try another entrance.
  • Rolls a 0, critical. Sooooo, what happens now? We'll see it with another d10 roll:
    • Rolls a 1, lucky success. Dorbud drops his lockpicking tool and when he picks it up notices a key laying on the floor. He tries it in the lock and it fits! Haha, it was never so easy!
    • Rolls a 2, critical success. It only takes 30 seconds before Dorbud is in, leaving no trace of his presence.
    • Rolls a 5, critical failure. Oh dear, he messed it up! Frustrated due to his inability to open the lock, he tries to kick the door down. The door didn't budge and now Dorbud has a sore foot. Besides, the noise might have alerted the guards...
    • Rolls a 9, lucky failure. Just when he almost had it opened, a small dog aproaches and starts barking surprisingly loud. Dorbud is forced to run for his live before the guards get him.
    • Rolls a 0 again. This is going to be epic! Let's roll the die again!
      • Rolls a 3, double critical success. Just like in the movies, Dorbud introduces the lockpick and in a couple of seconds the lock opens with a faint click. The guildmaster would be very proud of Dorbud if he saw this.
      • Rolls another 0, yet another 0 followed by a 9. ¡¡¡Cuadruple lucky failure!!! Lightning strikes poor Dorbud, who falls to the floor and takes a lot of damage. The lockpick gets stuck in the lock both being rendered useless. A nearby hay cart gets on fire, and everyone in the mansion is waking up and coming to see what has happened.

So that's all (well, most at least). If you're still interested, keep reading.

Rolling the die[edit]

You have an attribute/skill/whatever usually ranging from 0 to 9 that you need to test in a given situation. You roll one standard ten-sided die : If you roll a number from 1 to 9 you compare it with your attribute.

  • If you roll less or equal than your attribute you get a success.
  • If you roll more than you attribute you get a failure.
  • However, if you roll a 0 (also labelled 10 in some d10 dice) you get a critical result, which can be either very good or very bad. To determine it you have to roll a second die.
    • If you roll a number from 1 to 9 you compare it with your attribute.
      • If you roll less or equal than your attribute you get a critical success.
      • If you roll more than you attribute you get a critical failure.
    • If you roll 0 again you get a double critical result. Rolling a third die will determine whether it is a double critical success or a double critical failure. Of course getting more 0's would yield triple criticals, cuadruple criticals and so on.

Automatical success and failure rule[edit]

The die roll represents how well or bad the character fares using his existing attribute in a given situation. But sometimes external unpredictable events can determine the outcome in spite of the character effort and skill.

If a 0 is rolled (critical result), then :

  • If you roll a 1 you get a lucky success regardless of your attribute score.
  • If you roll a 9 you get a lucky failure regardless of your attribute score.
  • If you roll a 0 (double critical result) you can then get double lucky success by rolling a 1 or double lucky failure rolling a 9, and so on.


The open-ended d10 roll is technically equivalent to the Runequest d100 roll where a score of 1 would become a 10%, a score of 2 a 20% and so on. Everytime there is a 10% probability of getting a critical result, just in Runequest (for example, if you had a 40% you would get a critical sucess with 01-04 and a critical failure with 95-100 in your d100 roll, it is the same probability-wise).

There is also a resemblance with the Rolemaster open-ended d100 as double (1% chance), triple (1 in 1000 chance), cuadruple (1 in 10.000 chance), etc. criticals can be generated, so truly glorious rolls can happen.

Simple roll (Optional)[edit]

Sometimes you just need to know if the task is performed or not, without caring about critical or lucky results. In that case make a simple roll by ignoring any 0's you get, just roll again. If your attribute score is 0 or less you don't need to roll because you fail automatically; similiarly, if it is 9 or greater you are automatically succesful. This can speed things up with routinary tasks.

Degree of Success (Optional)[edit]

On the other hand, sometimes you need to gauge how well you perform a task, for example when you compete against other character (as in 'he who throws the stone further wins'). A critical success is always better than a regular success (and a double critical better than a regular critical, etc.) as it is to be expected, but you can also compare two successes against each other, the greater the roll the better the task is performed.

In fact, if you get a success the number you get in the die is called the degree of success, which you can compare against your opponent's degree or even against a difficulty degree set by the Game Master. If you get a critical success your roll is called degree of critical success and so on. Even a degree of failure can be considered when opportune, the lower the degree the worse the failure is.

Beyond Success (Optional)[edit]

In a roleplaying game sometimes truly amazing and extraordinary challenges await the main characters. The Game Master can require a critical success or even a double or greater critical success in order to achieve such deeds. Be aware that your chances of getting a double critical success are only 1 tenth of getting a critical success, and that is 1 tenth of getting a success, so they're dropping exponentially.

A high attribute score is no longer enough to cope with these situations, so heroic characters can attain mastery ranks, each of which allows to shift a failure result into a success, a success into a critical success and so on. In order to get a mastery rank a character first needs to get his attribute score up to 8. Only then, if he keeps developing the attribute, can get the rank, but his attribute score is reset to 1 and he would need to learn even more and more to rise it up.

Fine Grain (Optional)[edit]

If you feel that you need more precise scores for attributes you can use a decimal number, as in '5.3'. When you need to test the attribute score just roll ignoring the decimal (in the example roll under or equual 5 to get a success). But, if you happen to roll and miss by one single point (in the example getting a 6 in the die), you can try to 'push' your attribute score for that roll only: roll another d10 and if you score equal or under the decimal number (3 in the example) you manage to success (so, if you roll a 2 you 'push' your attribute score from 5.3 to 6 and thus get a success).

This fine grain system is probability-wise equivalent to rolling a d100. I just think it's faster and more interesting to roll dice this way. You can also combine both regular and fine-grain attributes with this system, focusing in the more interesting things.