D12 Dungeon Crawl System
The D12 Dungeon Crawl System is a game-agnostic Tension-based system for handling dungeon crawls, both for group and solo play. The Tension system means that a Tension value from 1 to 10 is kept track of by the Game Master throughout the dungeon, and the higher it is, the more dangerous things get. This simulates the fact that the longer the party stays in the dungeon, the more dangerous it gets because more and more of its inhabitants will realize that something is up. For the basics of the Tension system, please refer to the D12 Tension System article.
Any time the party gets into combat or otherwise makes noise, the Tension level goes up. And any time they accomplish an objective, circumvent a trap or discover a secret, the Tension level goes down. It is in the party's interest to keep the Tension level as low as possible, because when it increases - so does the danger.
It is up to the Game Master to decide whether this should be a player-facing system or not. Some groups prefer to know that such rules are in use, while others prefer to have such mechanics fully behind the Game Master's screen.
How to prepare a dungeon for use with this system
This system requires two tables for each dungeon:
- A Random Encounter table
- An Environmental Effects table
Let's go through them one by one.
Preparation Step 1: Make a Random Encounter table
The Random Encounter table should be a Random table with Tension, as explained in D12 Tension System. In short, this means that the all entries should be sorted by danger level, with the most dangerous encounters at the end of the list. Please note that while the entries should go from 1 through 20, you don't need 20 separate entries if you don't want - you can keep them in ranges.
Let's have a look at an example. This one is short for clarity - on a real Random Encounter table, you probably want to have more entries.
Example Random Encounter table
| d10+Tension | Encounter |
|---|---|
| 1-4 | A lost adventurer |
| 5-8 | 1d4 goblins |
| 9-12 | 2d4 goblins |
| 13-16 | 2d6 orcs |
| 17-20 | 4d6 orcs |
Preparation Step 2: Make an Environmental Effects table
An Environmental Effects table should contain entries which either create atmosphere, gives the PCs useful information about the environment, or has an otherwise interesting effect. Note that this table should also be sorted by danger, with the most dangerous - or ominous - entries at the end. Let's have a look at an example.
Example Environmental Effects table
| d10+Tension | Effect |
|---|---|
| 1-2 | 2d6 hidden gold pieces glimmer in a corner of the room |
| 3-4 | Tracks lead toward pre-set encounter |
| 5-6 | A fresh breeze indicates direction to nearest exit |
| 7-8 | Slime tracks on the walls hint at oozes lurking nearby |
| 9-10 | Unnatural draft makes torches flicker |
| 11-12 | Pocket of toxic gas released, Con save or 1d6 poison dmg |
| 13-14 | A tremor makes roof tiles fall, Dex save or 1d8 blunt dmg |
| 15-16 | Sudden drop in temperature - something approaches |
| 17-18 | Gas release makes air unbreathable, forcing all to move |
| 19-20 | Structural collapse blocks an exit |
With the Random Encounter and Environmental Effects tables complete, you're now ready to run your dungeon.
How to run a dungeon with this system
Any time the party enters a room with no pre-set encounter, or lingers in one location, (e.g., searching for secrets, investigating, or resting), the Game Master does two things:
- Roll on the Dungeon Events table
- Check if there is a Random Encounter, and if so, roll on the Random Encounter table to find out which one
1. Roll on the Dungeon Events table
First, we need to roll on the Dungeon Events table, to check if anything is happening.
| d12 | Event |
|---|---|
| 1-5 | Nothing happens |
| 6 | Non-magical light source fails |
| 7-10 | Roll on Environmental effect table |
| 11-12 | Enemies / NPC sounds (if appropriate) |
After you've rolled for this, but before you reveal the result to the party, you should also check if there is a Random Encounter.
2. Check if there is a Random Encounter
Roll 1d12.
If the result is:
- Less than or equal to the number of exits/doors in the room, or…
- Less than or equal to the current Tension level…
… then a random encounter is triggered. Roll on the Random Encounter table you prepared in Preparation Step 1 above, then run the encounter.
If there is both a Dungeon Event and a Random Encounter, then incorporate the event into the encounter. "Just as you notice your torch flickering out, you hear the unmistakable sound of claws against the stone dungeon floor as monsters take the opportunity to attack under the cover of darkness. Roll for initiative!"
Notice that the number of exits or doors in a room affects the risk of a random encounter. There's a greater risk of running wandering monsters in a grand hall with many doorways than there is in a storage room with only one exit.
If the party defeats an encounter, then strike it off the list. If you get the same encounter on a subsequent roll on the Random Encounter table, then there is no encounter; this reflects the fact that there probably isn't an infinite supply of encounters in the dungeon. This means that if you want there to be three different goblin patrols in the dungeon, then let each of them have its own entry on the Random Encounter table.
When to increase the Tension value
Certain events, such as combat and other noisy activities, increase the Tension.
| Event | Tension change |
|---|---|
| Breaking down a stuck or locked door | +1 |
| Relatively quiet, stealthy combat | +1 |
| Normal combat | +2 |
| Combat when an enemy escaped | +4 |
Other events can increase Tension too, at the Game Master's discretion. Remember that Tension can never be higher than 10. This means that even at its highest, the d12 roll to check for random encounters can still yield no encounter.
When to decrease the Tension value
Generally speaking, a low Tension value is beneficial for the party so it should be earned by accomplishing meaningful things.
| Event | Tension change |
|---|---|
| Disarming / circumventing a trap | -1 |
| Discovering a secret | -1 |
| Rescuing a prisoner | -2 |
| Achieving a major objective | -3 |
These are only examples, and the Game Master is of course at liberty to reduce the Tension for other reasons that they deem reasonable as well.
Designer's note: When I designed this system, I originally intended to have Tension decrease if the party managed to lock themselves away and rest somewhere in the dungeon without being detected; but then I realized that this would encourage too much caution which could adversely affect the game's enjoyability so I decided against that. Tension is a reward which should be handed out for accomplishments, not for hiding.
Tips for using this system
Here are a few things to keep in mind when using this system to give you better results.
Decide how much you want the players to know about the system
Some groups prefer to have full transparency with the mechanics behind the screen, while others do not. Know your group, and do what's best for them. But even if your particular group prefer to keep such mechanics behind the Game Master's screen, it might still be wise to say "Are you sure you want to rest here, with all these doors around? Aren't you afraid someone will come through here and discover you?" when they decide they want to rest in a well-traveled thoroughfare in the dungeon.
Provide opportunities to lower Tension
Since both combat and other noisy activities increase Tension, there must be a balance with the number of opportunities to lower Tension as well. To reiterate, Tension is lowered when the party accomplishes tasks, disarms or circumvents traps, and discovers secrets. So when you design your dungeon, make sure to provide such opportunities - add traps, prisoners to rescue, secrets to uncover, and so on.
But how many things should you add? Well, think of it this way - there should be about as much opportunity to lower Tension in the dungeon as there is to raise it. Unless, of course, you specifically want the dungeon to get increasingly tense the longer the party stays there, forcing them to leave the dungeon to reset its Tension?
Wait, what? Leaving the dungeon resets Tension?
Well, not just stepping outside it and then going back inside again. This isn't a computer game. Think of it this way: after the party has been in the dungeon for a while, more and more of its inhabitants will realize that something is up - and thus, the Tension increases to simulate this. If the party just steps outside the dungeon and then goes straight back in, that will change nothing. The goblins are still looking for them. But if they leave the dungeon and go back to town and return in a week, then that's probably enough to completely reset the dungeon's Tension. Things will then have settled down again - but on the other hand, by then the dungeon might be repopulated, or perhaps the inhabitants have built new defenses?