Venn Diagrams are unexplored as a way in TTRPG adventures to provide a unique kind of challenge to their players. Today, I’d like to present a framework for using these diagrams, to make the logic puzzles they provide more common. Any GM would benefit from this tool in their toolkit.

The concept came on my path when a friend ran a self-made mystery where we had to figure out which poison was used on a murder victim. We compare a list of possible properties against the things discovered on scene. It was amazing. The more I thought about it, the more opportunities I saw to implement similar puzzles into my own game. And now, maybe in yours?

Puzzles in Adventure Design

This blog uses the terminology as introduced by Boris, specifically that of keys and locks. In short: locks are obstacles that can be overcome through their key.

Constantly applying keys to locks becomes predictable after a while, where players might start searching for keys whenever they bump into a lock, instead of engaging with the adventure’s fiction. Open-ended locks extend their lifespan notably, but as the abilities of characters grow, so does their keychain. Certain keys might even prove too versatile and trivialize every lock. How then can we GMs keep the locks challenging?

This is where puzzles can come in. The difference to the key / lock solution is that there is no key yet. Players have to strip away possibilities until a key presents itself. Semantics maybe, but necessary semantics to help me visualize what puzzles contribute.

For Example: One classic is a chess puzzle, where players have to check the opposing king in a number of moves to open a door. No amount of spells or abilities would be able to help you here.

Why Venn Diagrams?

Puzzles are difficult to make feel natural or diegetic. A sudden chessboard in the middle of a dungeon feels off. Venn Diagrams are a more natural occurance. Mysteries often use them. As I’ve encountered the diagrams, they present themselves in a more diegetic language than most puzzles do.

For example: players need to assassinate the red knight. They know he: is allergic to wine; has a secret mistress; is invulnerable to fire. At a party, 4 persons could be the knight, and every one of them has 1 of these properties. Only the red knight has them all.

This puzzle has certain advantages (that are true for many logic puzzles a GM could conjure up):

1. Each piece of information isn't immediately obvious, but is discoverable in a natural way
2. Creative solutions are necessary to unveil the properties.
3. There’s a scalable difficulty through the number of possibilities and the pieces of needed information
4. It’s system-neutral in essence, but the logical elements could easily consist of system-specific mechanics (i.e. damage types for D&D 5e)

How I Applied One Myself

In our latest dungeon, the central conflict revolves around finding the correct spice vendor. My friend suggested a double layered Venn Diagram, either layer having the vendor at their center. Through this, players can also combine the diagrams, giving them more freedom in how to solve the puzzle.

A discovery we made is that it's more interesting to have a different approach for each diagram. One revolved around inquiring about the characteristics of the vendor. Whether he's male. Whether he's blond. The other revolves around experimenting on his wares. Players would know that the vendor’s spices dissolve in water, for example. Although given upfront, this knowledge requires action in order to become useful.

Now players have a dynamic puzzle that is applicable through any combination of social encounters and interactions with the environment. Of course, gathering the pieces of information or performing actions to test this information should come at a risk.

Not Solving the Puzzle

Venn Diagrams like these mainly challenge the players, not the characters. On a meta level, it could be difficult to justify why the wizard with super-human intelligence can’t break the code. I wouldn’t advocate reducing a puzzle down to a roll though. The fun stems from this meta-level of problem solving.

But… I would advocate to consider adding a failsafe. Sometimes your adventure expects a backdoor to be opened. In those cases, the solution should come with a severe consequence. Combat is a well-known failsafe, but depending on the situation I like to use several kinds of consequences:

• The party’s standing to another faction falls.
• Someone close to the party is harmed.
• The party loses access to an important resource.

Specifically, in the Bazaar adventure described above, the failsafe is triggered when the guards are alerted by presence and intentions. This unmasks all guards disguised as vendors, therefore leaving only the real spice vendor standing. Whether that spicer even wants to trade with a party in that situation (having an equivalent to 5 starts in GTA) is highly questionable

What I Hope You’ll Take Away

This blog intended to show how dynamic venn diagrams are. Honestly, I believe it only scratches the surface. Please, experiment yourselves! Share your experiences down below:

(How) Have you encountered logic puzzles before in TTRPG design? If so, which takeaways do you still carry with you?

I’d love to know!

Cheers,
Willem-Jan

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