Megadungeon Practical Example 4: Random Encounter Theory

No megadungeon is complete without bespoke random encounter/wandering monster tables, but this requires some unpacking. A good dungeon random encounter table has to achieve the following:

1. It should be bespoke, but not too bespoke

2. It should be level-appropriate, but not too level-appropriate

3. It should reflect the contents of the respective dungeon level, but not too much 

Let's deal with each of those in turn.

First, it probably goes without saying that it is important that random encounters should not be entirely 'random' in the sense that just any old monster could show up. Each dungeon level should have its own table, and it's best if the entries within it are unique to it and don't show up on other levels, and area also interesting things to come across in their own right - not just goblins, wolves, yellow mold and so on. At the same time, though, it's also fine to have some wildcards - there's nothing wrong with a generic monster or two appearing in amongst all the wonderful special snowflake entities you've made up, and indeed it can be refreshing to suddenly come across some orcs or a dragon in among all the owl-man automatons and phthalo rhinoceros ghosts. 

Second, it has long been a principle of D&D that encounter tables in dungeons are level-appropriate, and those in wilderness areas are not. Dungeoneering should in this sense be a bit more predictable and manageable than wilderness travel - broadly 1 HD monsters on level 1, 2 HD monsters on level 2, and so on, with some variation (a single 4 HD monster could appear on level 1, for example, as a roughly appropriate challenge for a party of 1st level adventurers).

However, I am also a believer that things should not be too predictable, and that it keeps the PCs on their toes if it is occasionally possible to encounter something that is genuinely too powerful. For this reason, I tend to stock my tables with non-level-appropriate monsters in the 'very rare' result range (see below). 

Third, the table itself should be stocked with monsters that are broadly thematically appropriate in view of the contents of the dungeon level itself. Hence, for example, in level one of Lost Eskinoot, there is an aviary, a forge, a kiln, an area of water contraptions such as wheels and pipes, and a parkland containing many statues. This suggests a random encounter table containing monsters that are broadly appropriate to those kinds of environments.

But at the same time, the contents of the random encounter table should avoid being too 'matchy-matchy'. Some years ago my wife and I got caught up in watching a series about interior design. A fabulously flamboyant and loveyish expert would show up each week to express her opinions, and she was always stridently opposed to designs making use of the same pattern on different objects in a room (for example, on the wallpaper and on the sofa). Tasteful use of the same colour was fine, but using exactly the same pattern would be condemned for its 'matchy-matchiness'.

By the same token, I am not a great believer in stocking a random encounter table with the same monsters that will be encountered in the actual rooms of the dungeon. They should be thematically similar, but different. Hence, for example, the kiln area in Lost Eskinoot is home to mephits. This means I would not have mephits appearing as random encounters - but I might have, say, dweomerlings or (clay) mudmen. This maintains thematic consistency but keeps things fresh.

The results of applying these principles are random encounter tables that feel 'right' in the sense that whatever is encountered does not seem totally out of place in a jarring way, but which does contain some 'crackerjack' items that will genuinely surprise, delight, and/or terrify the players.

A final word on structure. Some people use a straight 1d12 or 1d20 table, but I prefer to use 2d6, which gives a bell curve of frequency of results. This means that monsters in the 5-8 results range will appear more frequently than those at 2 or 12, and allows the incorporation of 'very rare' extra powerful encounters at the extremes. If this has the effect of making things a bit samey, one can easily remedy the problem with sub-tables for the common results. Hence, a typical random encounter for a level 1 dungeon (let's use Lost Eskinoot) might look something like this:

2 - Spectral artificier (treat as 'Spectre')

3 - Vegepygmies 

4 - Dweomerlings 

5 - Giant frog or newt

6 - Giant arthropod (1 - Crab spider, 2 - Giant centipede, 3 - Cave cricket, 4 - Giant wasp, 5 - Fire beetle, 6 - Oil beetle)

7 - Humans (1 - Outlaws, 2 - Bandits, 3 - Merchants, 4 - Vagrants, 5 - Sages, 6 - Cultists)

8 - Mammals (1 - Jackals, 2 - Giant bats, 3 - Baboons)

9 - Mudmen

10 - Kobolds

11 - NPC adventuring party

12 - Gargoyles