I’ve previously posted about methods using playing cards for wilderness and night travel hazards; now I’m going to take a look at using the same method for the most classic hazards of all — dungeon random encounters. There’s going to be a tiny bit of math in this post, which is to say there will be numbers, which is likely far more intimidating to me than it is to you.

First, let’s get a baseline for how common dungeon random encounters are using traditional dice-based methods. DCC RPG doesn’t provide any rules that cover this, so let’s assume the tried-and-true standard from Labyrinth Lord (i.e., B/X): For every two turns elapsed, the DM rolls 1d6 and an encounter occurs on a 1. This works out roughly to a 16.7% chance of an encounter per two turns, or roughly 8.4% per turn.

When looking at the probabilities of the cards, I’m going to assume 54 cards in the deck (Jokers left in), since that’s what I’m using for wilderness hazards. Ideally I’d like to draw a card every turn rather than every other turn; it just seems simpler to me. Check off a box for light sources, draw a card and check for encounters. Also, I don’t intend to reshuffle the deck until the PCs leave the dungeon. This means going through the full deck equates to 9 in-game hours spent dungeoneering, which makes for a really convenient way to know when the party is starting to need serious rest.

The chance of drawing any one card from a 54 card deck is 1.85%, therefore the closest results I can get to the 8.4% chance provided by the d6 are 7.4% if four cards generate encounters or 9.3% if five cards generate encounters. Of those two, I would lean toward the four-card option for simplicity sake — a face card or ace from a single suit corresponds to an encounter. Easy.

But I’m not going with either of those options. Instead, I am going to say that, at the very least, a face card or ace from a single suit and the two Jokers correspond to encounters. This ups the chance per turn to 11.2%, an increased likelihood of 33%. Besides just wanting to beat up my players, why am I doing this? I am doing it because under the card method the chance of further random encounters changes as one draws the cards that correspond to encounters.

Using the d6 method, the odds of a random encounter on any given two turn sequence never increases or decreases. Using the card method, however, if two of the six encounter cards come out on the first two turns of exploration, then the chance of an encounter on the subsequent turn has dropped to from 11% to 7.7%. The statistical pendulum can also swing the other way, of course; if the PCs have still only faced two of the six encounters 20 turns into dungeon exploration, the chance of a random encounter on turn 21 has increased to 11.8%. If they get all the way to turn 40 and luckily manage to avoid any further random encounter beyond those first two? The chance of a random encounter on turn 41 is 28.6%.

This is one of the things I love about the card method: Given enough time exploring the dungeon, the number of random encounters is both finite and inevitable. There are only so many beasties that are wandering a given level of the dungeon at a time, but hang around down there long enough and no matter how careful you are, you’ll eventually attract their attention.

Next time I’ll look at another reason I like the card method — the same card that determines there is an encounter can also determine what is encountered.