Content of the article: "The Generator Puzzle (or: how to defuse a bomb submerged in magma without setting off the volcano)"
Greg, Max, Wes–turn back now, this is not for you.
Hey all! I'm running a Pokemon 5e oneshot for some friends tomorrow (shout out to Joe the DM and the rest of the P5e crew), and the "puzzle boss" of the game is a generator submerged in the magma of Mt. Chimney that the PCs have to deactivate without disturbing the volcano too much. This can be repurposed for any setting–the generator can be a sleeping behemoth and pressure valves can be warding circles, for instance, or an antimagic bomb and the sigils keeping it contained, or whatever you desire.
There are 3 elements to the puzzle: the Pipes, the Manual, and the Terminal. Each of these is found on a different part of the map surrounding the central generator, close enough to shout across the distance but too far to run between locations in one turn. I have them spaced 85 feet apart. We're using roll20, so each element has its own map that a player will only be able to see if and when they are stationed there.
In order to safely deactivate the generator, the SHUTDOWN.EXE program must be run from the Terminal when the system pressure of the Pipes is 0.
A network of pipes connects the Terminal to the generator, suspended directly above the magma of the volcano. Any character vulnerable to heat exhaustion must roll a CON save for each round spent working on the Pipes, taking a level of exhaustion on a failure; the DC is 10+(# of rounds spent at the Pipes). A character may reset the DC to 10 by taking an action for a "cooldown round" (by i.e. pouring water on their head) or leaving the Pipes area, which also takes a full round. Up to you if you want to introduce a resource management challenge here, or allow a canteen to have infinite cooldown uses.
There are 5 valves with wheels spaced among the pipes; I used this image. Give each wheel a number; these numbers should not initially be known to the players.
Wheels 2 and 4 change pressure; wheels 1, 3 and 5 change flow direction. Create a pressure dial, which should be visible to the players; it starts at 2. (Make up whatever units you want; I'm using milliVolcanions per square inch). Also assign a "default flow" to each of the odd-numbered wheels–when the puzzle begins, two should be inflowing, one outflowing.
Even wheels can only be turned when system pressure is equal to or greater than their number. Odd wheels can only be turned when system pressure equals their number. So, at puzzle start, only wheel 2 can be turned; attempting to turn any other wheel is a wasted action and possibly damage. One turn of the wheel = a change of 1 mVpsi; an action can be taken to turn a wheel up to 5 times. The system will repressurize at a rate of 0.5 mVpsi per round if it left unattended below 2 mVpsi.
Turning an even wheel will either increase or decrease system pressure depending on the average flow direction of the odd wheels. If 2/3 odd wheels are set to inflow, turning an even wheel will increase pressure, and vice versa. If all 3 odd wheels are ever set to the same flow direction, an emergency valve vents boiling steam, dealing <3*system pressure>d6 fire damage to everyone within 10 feet, DEX save for half. If someone attempts to turn an even wheel at the wrong system pressure, they are burned by the hot metal for the same damage, CON save for half.
So while it's technically possible for the players to turn the wheels in exactly the right order with no further information, realistically that would never happen. That's where the other parts come in.
Documentation regarding the generator's operation and maintenance can be found scattered on the tables and corkboards of a nearby structure. It is all extremely complex and detailed. (I will also put a couple of mid-tier trainer battles here, technicians trying to stop the party from messing with their gear.) Each round a character spends trying to read the documents, they may roll an Investigation check to find useful docs; each round after that, they may roll an Insight check to try and understand what they find. The Insight DC for a given document equals 10+(20 – Investigation roll for that round). High Investigation rolls result in difficult-to-find but clear and concise information; low Investigation rolls give them complex and incomprehensible diagrams. A character finds all items at or below the Investigation DC they passed; if they have not yet beaten the Insight DC, they may spend subsequent rounds re-trying. I recommend scattering images like this on tables throughout the map.
Investigation 10/Insight 20: all the information italicized in the previous section. They find a detailed diagram of the Pipes, but it's filled with jargon and unhelpful symbols and requires a genius to understand.
Investigation 15/Insight 15: the text of the Solution section above. They find startup/shutdown instructions, but they are written in a programming language that bears only a slight resemblance to Common.
Investigation 20/Insight 10: a numbered diagram of the wheels and the system's default flow (i.e. 1 and 3 out, 5 in). It is clear and informative, but has been obscured by another poster that has partially come unstuck from the wall.
So, a character might initially roll a 14 Investigation and 13 Insight; they would find the diagram but be unable to solve it. On their next turn they could either reroll their Investigation check to see if they find anything else, or reroll their Insight check to focus on deciphering what they have found. If they roll a 20 Investigation on the next round they will see all 3 potentially-useful documents, and their subsequent Insight roll will determine which of those they understand.
Finally, the computer terminal controlling the generator is located in a lab, at one end of the Pipes. (I'm putting a high-level trainer battle here, a senior engineer.) The terminal consists of 3 password-protected monitors, and a memo is sitting on the console indicating that a new encryption strategy has recently been put in place. The memo provides all 3 passwords, deviously encoded to prevent outside access. It takes an action to attempt a password entry.
This one you can play however you want. I have 3 simple Pokemon riddles, the answers to which are the decryption keys for the Vigenere ciphers that encode the actual passwords; that may seem needlessly baroque, but one of my players is a cryptography geek who I expect to ace this part no problem. (The memo is signed "Chief Technology Officer Vigenere.") Feel free to simplify as needed, you could eliminate the code part entirely and just have the passwords be the answers to the riddles.
Each terminal, when unlocked, gives access to a control suite that can decrease the puzzle's difficulty in a specific way. The first one gives access to a slider that can be used to reduce the temperature of the steam in the pipes; each round spent dialing this down subtracts one damage die from the "wrong wheel" punishment (maximum -2d6, can't be dialed to 0). The second one is an index providing the names and cover images of a few important documents, which if communicated to the player attempting the Manual will give them advantage on their next check (one round spent describing documents = one round of advantage). The third one controls the vents to the two ice pokemon enclosures on the sides of the volcano; the player can take an action to open a vent, cooling down the air above the magma. Each vent opened grants a one-round grace period between a cooldown round and starting the CON saves at the Pipes, and subtracts 1 from the DC of those saves.
Entering one incorrect password results in the Terminal's Porygon-Z cyberdefense platform firing a Thunderbolt at the user (you can use a Lightning Bolt spell if you like). Entering a second incorrect password results in a Zap Cannon (or upcast electric-damage Fireball). Entering a third incorrect password results in the Porygon-Z manifesting from the computer and attacking; additional incorrect attempts result in additional Porygons-Z. Five incorrect attempts causes the terminal to short-circuit (making the puzzle impossible to complete).
Finally, SHUTDOWN.EXE can only be run if at least one password has been correctly entered. Attempting to run SHUTDOWN.EXE when system pressure is not at 0 has the same effect as an incorrect entry, while also venting steam from all of the wheels on the Pipes.
It's a lot I know, but hopefully when put together it will flow well. Once all the opposing trainers have been defeated & scared away, I intend to have the party roll initiative and proceed through the puzzle round by round until they solve it or until 20 rounds have passed (and the generator explodes, dealing 10d6 fire damage and 10d6 electric damage to everyone within 500 feet), whichever comes first.
An example solution to the Pipes puzzle is as follows:
At start, wheels 3 and 5 are inflowing, wheel 1 is outflowing, and system pressure is 2. They have to change the flow direction of either wheel 3 or 5, and then reduce system pressure to 0 to run the command.
One round to increase system pressure to either 3 or 5 by turning wheel 2 once or thrice. One round to change wheel 3 or 5 from inflow to outflow. One round to decrease system pressure to 0 by turning wheel 2 or 4 (they can only use wheel 4 if they bumped system pressure to 5) thrice or five times.
Any feedback is greatly appreciated! This is definitely the most complex puzzle I've ever written, so I'm curious what folks think. Wheels 1, 4 and 5 are kind of red herrings as the whole thing can be done without touching them, but I don't think that's necessarily an issue (and of course watching your players second-guess their correct solution is one of the DM's greatest joys).
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