An ability test and Thief skill system for B/X

I’m actually doing it. I’m making my own version of what I think the Basic/Expert rules should have looked like, with dice rolls that are intuitive and level progressions that are consistent, based on my first experiences with the d20 system. I’m probably not gonna use it, and it’s really just an exercise in tinkering around. I don’t think you would get a lot of interested player for a campaign by a new GM with his personal fantasy heartbreaker, but maybe when I have an established OSE campaign running the players might be interested in a less messy version of the rules which still really do the same thing.

It’s really just all the Yora rules put together. Mostly ideas that come from Stars Without Number, Lamentations of the Flame Princess, and Deep Carbon Observatory. But I also got some original ideas of my own. (Which I’m probably not the first person to come up with.)

Where I think B/X really can be improved is some kind of consistent system for ability checks. Hear noise and detect secret doors are a 1 in 6 roll. Thief skills are a percentage roll. Other actions are suggested to be handled by rolling a d20 under the characters most relevant ability score. It’s all over the place. The solution that I’ve come up with is none of the above.

To make a roll to see if a character succeeds on an action that seems plausible to work but success is not certain and there are meaningful consequences for failure, roll 2d6 against a target number based on the character’s most relevant ability score.

For characters with no modifier for the relevant ability, the target number is 7. (Right in the middle for a 2d6 roll, the most common result, and a chance to succeed of 58%, slightly above half.) This number is modified by the ability modifier.

Score Modifier TN Chance
3 -3 10 17%
4-5 -2 9 28%
6-8 -1 8 42%
9-12 +0 7 58%
13-15 +1 6 72%
16-17 +2 5 83%
18 +3 4 92%

This system replaces the Strength modifier for opening doors. (2d6 against TN 5 is about the probability of 1-5 on a d6.) If a task seems particularly difficult, you can tell the player  to roll with -1 or -2, and the majority will intuitively understand that this means 2d6-1 against the same target number as always. (The target numbers should be on the character sheet, like saving throws.)

The very same system to make rolls can also be used to roll for Thief skills instead of 1d100 roll under. This assumes that Thief skills are things that are simply impossible for anyone who isn’t a thief. Climbing walls too smooth to climb on, moving without making any noise, hiding with nothing to hide behind. These are things you can’t take a shot at and hope to get lucky without the special training of the thief class. (For hearing noises, I would go with letting a thief roll against the target number of either his Wisdom or Thief skill, whichever is lower.

Hit point increases in B/X

I somewhere saw people discussing the question whether the thief in B/X would be better having a d6 for hit dice instead of a d4, and one point that was brought up against that is that the thief gains new levels very quickly and as such has more Hit Dice than other characters with comparable XP, and that this would even things out already.

I’ve long felt that the speed of thieves gaining new levels has been greatly overstated, and so I went to check how the average hit points over time for the different classes actually look like.

Average hit points from 0 to 32,000 XP.

As can be seen here, a thief’s average hit points do get very close to those of a cleric on reaching 4th and 5th level, but the cleric almost immediately surges ahead again.

Average hit points from 0 to 640,000 XP.

And after those initial first levels, the gap between thieves and clerics only widens until 10th level when the cleric continues to gain only 1 hp each time compared to the thief’s 2 hp. Now a 6 hit point gap on average towards the end of the B/X progression is not that big, but at these small numbers that’s still +20% for the cleric. And a +50% for the fighter, compared to the thief.

Does that make thieves too fragile at higher levels? I don’t know, I’ve not enough experience at play at those levels. But I think this also shows that the thief’s faster level advancement rate does not negate the difference in Hit Die size to the cleric at all.

Random hit point ranges

A few years ago I read something about the value of always rolling for the hit points of creatures and NPCs that the players get to fight and not always taking the average by default. I really like the idea of using different hit points to give individual opponents a bit of a personalized description even though otherwise they have completely identical stats with the same AC, saving throws, hit chance, and damage on a hit. In a fight against some random orcs or bandits, it can be a neat and convenient inspiration to have those with 7 hp look much larger and more menacing and approach the fight different from their otherwise identical buddies with only 2 hp.

But sometimes, you might want to know what actual hit points numbers might be realistically expected for a given number of d8s. So I made this little table. The math magic behind calculating 2 standard deviations for normal distributions isn’t really important here. What this table shows is the range of hit points into which 96% of all random rolls will fall. There is only a 2% chance that a randomly rolled number will be lower than the shown range, and a 2% chance that a number will be greater. It will still happen occasionally, but even then most likely only by 1 or 2 points, and for the purposes of encounters in an RPG, I consider the odds negligible. You can just assume that pretty much all randomly rolled hit points on a d8 will fall into the shown ranges.

Hit Dice hit points
1 HD 1-8
2 HD 3-15
3 HD 6-21
4 HD 9-27
5 HD 12-33
6 HD 16-38
7 HD 19-44
8 HD 23-49
9 HD 27-54
10 HD 31-60
11 HD 34-65
12 HD 38-70
13 HD 42-75
14 HD 46-80
15 HD 50-85
16 HD 54-90
17 HD 58-95
18 HD 62-100
19 HD 65-105
20 HD 70-111