Encounter Table Basics

A guide to creating encounter tables

I've decided that January is "Make Your Own Island" month. This started out as me puttering about with some encounter tables, but things escalated quickly, and I decided to turn it into a fully-organic, quick-and-dirty summary of how you can create a little campaign setting. In last week's post, I ended up creating an island map and broached the concept of nested encounter tables. More on that below, but first...

Some Housekeeping

Isle of Minocra

Minocra (1 hex=5 miles)

To provide a sense of scale, I added the Regional Hex template as an overlay to the MapGen2 map of Minocra. Last week's version used the CC3 version of the template, but before this exercise is over, I'll want to place some symbols on it, add some labels, and embed notes. All these things will be easier in Hexographer, so in keeping with the quick-and-dirty approach I'm after, the map at right is rendered with the Hexographer version of the Regional Hex template. The map itself is semi-transparent, so the colours don't "pop" as much, but it's a trade-off between making the map or the hex overlay visible. You can't make out the hex numbers, but you still get an idea of what's what.

Added bonus: this paves the way for creating a true hex-only map, which may or may not materialise—all depends on how jiggy I get with it. Now, back to the business at hand...

Nested Encounter Tables

As suggested in last week's post, the best encounter table is one that you customise for your setting and your group. In other words, you're defining the setting by the encounters in it, but with a particular eye for what challenges your players and keeps them interested. Put that way, an encounter table is more than just a roster of what the PCs might meet 1-in-6 times every few hours—it's really more of a blueprint for who lives in the setting and what they do there.

I like nested tables, which requires a multi-roll, drill-down approach to determining encounters. One of my favourite models is from the Rules Cyclopedia, which provides a chart for each terrain type, and the results lead to sub-tables of different monster types—not, as might be expected, actual monsters. For example, if you wanted an encounter for grasslands, you'd roll on the "Plains" table, which might give you a result of "Insect" or "Human." Then you go to the appropriate sub-table, where you roll again to see what Insect or Human actually shows up.

This is where the format becomes useful. Instead of interpreting "Insect" as an actual monster, think of it as an encounter type. Now the Insect sub-table can include any manner of bug-related stuff.

With that in mind, the last tweak is weighting the table to reflect the odds of one encounter occurring over another. The original RC encounter tables were equal-distribution—there were 8 results, and you rolled 1d8 to determine which one you got, meaning that each entry had a 12.5% chance of coming up. This is fine if you want equal odds, but I suggest you weigh your top-level encounter tables because it makes it easier to devise encounter types.

Chimera provides some guidelines for monster frequency, suggesting Common (40%), Uncommon (30%), Rare (20%), and Very Rare (10%). You can apply these frequencies in general terms and create tables using 1d10 or 1d20, like this:

Die Range (1d10) Die Range (1d20) Frequency Encounter Type
1-4 1-8 40% Common
5-7 9-14 30% Uncommon
8-9 15-18 20% Rare
10 19-20 10% Very Rare

Note that your table need not be limited to 4 results: don't confuse frequency (as a percentage) with roll result (as a single number). What's important to remember is that Common encounters occur 40% of the time represent 40% of the table's composition.  That means, on a 1d10 table, 4 out of 10 results must be Common. This could be a single Common encounter in the 1-4 range, giving you a 4-in10 chance of a Common result when you check the table.

If you need more "slots" on the table, you might split that 4-in-10 chance into roll results 1-2 and 3-4, or even 1-3 and 4. It really doesn't matter how you arrange the table entries, so long as Common entries don't occupy more than 40% of the possible roll results. However, doing this changes the probability of those results coming up (e.g., 1-2 equals 20%, 1-3 equals 30%, 4 equals 10%). So while your table's composition is 40% Common, the probability of getting a Common result might be less than that (thanks to Roger for pointing this out).

Alternatively, you can accomplish similar wizardry by rolling multiple dice and adding the results. This forms a bell curve, familiar to many gamers the world over, where results in the middle of the range occur more frequently than results on the extreme upper and lower ends. It works, and involves more math (albeit not very difficult math), but it can be time-consuming. You can get clever and use 2d6, 1d4+1d6, 3d10, whatever combination you want, but each combination offers up a different set of probabilities, and very few are going to be as tidy as the model shown above. My advice is to keep things quick and easy to create and maintain by sticking with 1d10 or 1d20 (or, if you're into big tables with lots of results, 1d100).

Thus, our revised sub-tropical jungle table from the last instalment might end up like this:

Die Roll (1d10)
Encounter (sub-tropical jungle) Sub-table Frequency
1-2 Animal Animal Common
3 Insect Insect Common
4 Plant Plant Common
5-6 Human Human Uncommon
7 Sub-men Sub-men Uncommon
8 Event Event Rare
9 Monster Monster Rare
10 Unusual Unusual Very Rare

From this, you would generate sub-tables for each Encounter Type. When you make sub-tables, the frequency variation is up to you. My rule of thumb is this: if the table has a sub-table, I use the distribution above. But if the table is final (i.e., there are no sub-tables), I use equal-odds distribution. Continuing with our example, if I get a 3 on the table above, I roll on the Insect sub-table:

Die Roll (1d10)
Insect Type
Sub-table
1-4 Crawler Insect (crawler)
5-7 Flyer Insect (flyer)
8-9 Burrower Insect (burrower)
10 Parasite Insect (parasite)

Again, I'm creating encounter types, though they're limited to categories of insects. Because there are more sub-tables, I use a weighted distribution on the Insect table. But the remaining sub-tables Crawler, Flyer, Burrower, and Parasite) are the end of the line, so I'll use an equal-odds distribution for each. Here's the Crawlers sub-table, which uses 1d6:

Die Roll (1d6)
Insect (Crawler)
1 Ant, giant
2 Beetle, luminary
3 Beetle, tiger
4 Rock Mantis
5 Spider, hunting
6 Swarm

Final Words

We're just touching the tip of the encounter table iceberg, and there are a few more details I'd like to add to the mix in the next instalment.

As a side note, my apologies for missing last Wednesday's post. These are busy times, and I've been heads-down ramping up my new Chimera RPG offering, which will happen by the end of the month.

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