Wandering monster percentages

I just did an analysis of the wandering monster distribution over hit dice in Moldvay B/X.  I did this because I wanted to make sure my own wandering monster tables were "fair" - not overloaded with high hit dice creatures.

So here's the raw data.

First level: 15% 1/2 HD, 60% 1 HD, 20% 2 HD, 5% 3 HD
Second level: 20% 1 HD, 60% 2 HD, 15% 3 HD, 5% 4 HD
Third level: 5% 1 HD, 5% 2 HD, 45% 3 HD, 40% 4 HD, 5% 5 HD
Fourth-fifth level: 5% 3 HD, 40% 4 HD, 25% 5 HD, 25% 6 HD, 5% 7 HD
Sixth-seventh level: 5% 4 HD, 30% 5 HD, 40% 6 HD, 10% 7 HD, 10% 8 HD, 5% 10 HD
Eight+ level: 10% 6 HD, 5% 7 HD, 30% 8 HD, 20% 9 HD, 15% 10 HD, 10% 11 HD, 5% 12 HD, 5% 15 HD

Some of the monsters have hit dice ranges (hydras, hell hounds, etc) - for those I just used the hit die in the middle of the range, and if it was even, I picked a direction one way or another.  So there's some imprecision there.  For adventuring parties I gave their hit dice the same as the level.  Again, things are picked arbitrarily for the "fourth-fifth" multi-level tables.  If creatures are "+1" or "-1" or whatever to hit points, I don't care, they're that many hit dice.

A few observations:

a. Wandering nobles on the first level of a dungeon?  That's a little peculiar.  Maybe there was an assumption that dungeons are located under active, working castles, and of course nobles would occasionally head down to find the wine cellar or something?
b. Adventuring parties first start showing up on the wandering monster tables at level 3.  About where I was thinking of placing them in my own megadungeon.
c. The dungeon wandering monster tables really fall apart as you go up in levels.  You can definitely tell the focus turns to wilderness exploration and other non-dungeon-focused encounters.  There's just not a heck of a lot of effort in providing a variety high-level dungeon opponents.  Well, boo hiss to that.  Wilderness is fun, but don't abandon your roots!

So if I look at this data as # of creatures at -1 level, dungeon level, +1 level, +2 or more levels, I can put together the following table showing the distribution:

Level-1 HDAt Level+1 HD+2 HD or more

For the 8+ level, I treated 8 and 9 HD encounters as "at level".  For the "average" row, I rounded to the nearest 5%.

Now I like to use 2d6 for my wandering monsters, rather than a d20.  The curve means that more common monsters come up more often.  So if I roughly map those results to a 2d6, I get the following table:

2-3+2 HD
4+1 HD
5At level
6-1 HD
7-9At level
10+1 HD
11+1 HD
12+2 HD

And here's the distribution (in percentages) of my existing wandering monster tables:

AreaNon-combat-1 HDAt Level+1 HD+2 HD or more
Level 117%0%55%25%3%

Now I have an extra category of "non-combat" encounters that B/X doesn't have (spooky noises, etc).  Of course I don't have any encounters at -1 HD.  Comparing to the "average" table, it looks like my wandering monster tables, done entirely by "feel," are fair.  Probably slightly more than fair, since I've got those non-combat encounters instead of lower hit dice encounters.

In other news, I've got the cover art back from Brian "Glad" Thomas and will post that at some point, it's awesome. I'll be getting some interior art done as well, I need to figure out how much - the point of releasing the first level is to fund more art for the next, and so on, and so on... so while I'd love to have everything illustrated to the hilt, I do want to at least break even on the thing.

The "setting" type content is almost done. Just a few sections left to write, and then I want to write up a bunch of interesting NPC's. A friend gave me a copy of City-State of the Invincible Overlord, and while I think that supplement is overkill for how I run a city, I can see the utility of having piles of NPC's, their goofy motivations, and random details, for when the party begins to wander aimlessly. So I hope to have everything written before the end of February, and then the editing & layout begins. That's a good thing, because my players are on the cusp of heading down to level 2, and I need to get working on that.


  1. Interesting stuff, saved it to check against my by-my-gut charts. Thanks for sharing.

  2. Perhaps the nobles are second or third sons out hoping to be granted titles because they're so unlikely to inherit? A bunch of bored idiots looking for something to relieve tedium?

  3. You mean like these guys?


  4. Excellent analysis. Quick question on using HD as the 'power category' - did you notice any correlation with 'asterisks', HD, and power level?

    (My quick check said No - the Moldvay charts primarily use HD as the factor regardless of how tough the monster *really* is due to special abilities).

  5. Pat - another quick question - how did you embed those awesome tables? I thought they were images at first.

  6. Really useful data here -- I usually construct my own WM tables by feel as well, and am unafraid to "stack the deck" a little in terms of increasing probabilities for certain monsters to appear. But your charts here make an excellent baseline for estimating this stuff, THANKS!

  7. I did the tables by entering raw HTML, you can go to the "Edit HTML" tab in blogspot when you're making a new post and enter whatever HTML you want.

  8. Oh, and I totally ignored the asterisks. It's just HD.

  9. Great stuff, Pat: I'll have to compare your analysis against the WM chart templates that I built for my Castle Greyhawk, and see how well I adhered to the HD +/- models you outlined here.


  10. Thanks for your work! Printed up for my B/X binder.