I'm GMing a 5e Dungeons and Dragons game, set in a Forgotten Realms-like world.

I want the party to enter a room and see something like a lever, that appears to be a reversible mechanism but once activated cannot be deactivated.

As there is a high risk of death due to this mechanic, I don't want the players to feel cheated with something as simple as "it's broken" or "it's locked in place", only to have me stop them from succeeding on any repair spell or strength check.

It's important to the story and the dungeon that this is not something they can reverse easily. If they manage to come up with a solution to whatever I decide to implement, then that's fine, but I don't want this to be designed with any solution in mind.

TL;DR: I need a mechanism that appears two-way, but is not reversible.

The situation

There is a room with a painting. In the painting is detailed the characters minus one (player or NPC, I don't know yet) as well as an unlocked and open door. There is no way to open this door in the room they are currently in.

Also detailed in the painting is an activated mechanism similar to the one found in the real room. The idea is that activating this mechanism will "switch" the room and the painting, opening the door but effectively trapping the character in oil pastel hell.

I'm planning on making it very clear that this will happen throughout the dungeon (this is nearer the end), and I don't want the players to be able to simply finish the dungeon, come back through, and then pull the lever again to bring the player back.

I also want this to at least seem fair to the players, rather than me railroading them into a death.

I'm considering simple having the mechanism disappear from the painting once they pull it, indicating that the mechanism is no longer affecting the painting, but I would prefer something physical that they can investigate and at least try to 'solve'.

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  • \$\begingroup\$ You might also consider posing this question in the Worldbuilding SE if you don't mind completely homebrewing the mechanism \$\endgroup\$ – convoliution Feb 27 '19 at 21:11
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    \$\begingroup\$ Welcome to RPG.SE! Could you provide more information on what this mechanic would do? There are lots of mundane mechanical devices that are one-way activated, and it's not clear what requirements you have for this device that would necessitate choosing one over the other. \$\endgroup\$ – Xirema Feb 27 '19 at 21:13
  • \$\begingroup\$ @Xirema I've updated the post with more information on the mechanic. \$\endgroup\$ – Moralous Feb 27 '19 at 21:29
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    \$\begingroup\$ I'm unsure what you mean by "switching" the room and the painting. Is it a magic trap that teleports them into a separate room (perhaps in a demiplane) that looks like the room in the painting? Or is it a physical mechanism, like a wall that spins around 180 degrees? Was it specifically built as a trap, or is it something that used to be a functional means of transport, that has become dangerous over through decades of neglect? If something was built as a trap, there's no reason to expect it to be directly reversible, or else it wouldn't be much of a trap. \$\endgroup\$ – Ryan C. Thompson Feb 27 '19 at 23:23

It works by breaking something, or using something up.

Flat stone tablet covered with runes somewhere in the floor. The mechanism engages and drops a pile driver to break it, causing the magical effect.

Thick copper wire, mounted in a glass cylinder, traced with spirals of paint. The mechanism engages and it vanishes in a cascade of sparks.

Thick glass vial filled with an iridescent blue mist. On activation it's sucked into the machine. It does not replenish.

Somewhere deeper in this complex is a workshop with notes discussing how to create more of this stuff. Maybe there's even a note in the empty space saying "see Bovril for spares", and who the heck even is Bovril? Can the party find it, or work out how to make more?

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    \$\begingroup\$ These are all good tips. Honestly, a trap that is "self-resetting", though a common adventure trope, is way harder to engineer than a one-time-use trap! \$\endgroup\$ – Master_Yogurt Feb 27 '19 at 23:18
  • \$\begingroup\$ These are all amazing ideas - I specifically love the last one, as resurrection quests are a favorite in my group \$\endgroup\$ – Moralous Mar 2 '19 at 22:07

Here's a few ideas for how the mechanism might be interacted with without a clear victory scenario:

1: Out of Time

Activating the mechanism switches the rooms, but also triggers a trap that creates notable urgency for those who are safe. Something where there is a theoretically possible solution, but reversing it takes enough time that they will have to save themselves and leave their friend to their fate. Could be anything from the room filling with sand, walls closing in, or powerful enemies attacking.

2: Rising Stakes

Activating the mechanism isn't trivial, and requires some knowledge to pull off correctly, and isn't the same every time. Perhaps each attempt puts either the captive or the "safe" people at increasing risk, and the odds are heavily against them figuring it out. For every failure, maybe the paint hardens until solid, or the walls compress in more on everyone.

3: Prisoner Exchange

Activating the mechanism again switches the person who pulls it with the person in the painting, so that someone must always stay behind. Becomes a challenge of either selfishness or selflessness. Could potentially be overcome by forcing some other creature to pull it, though you could set limits to living/sentient or something.

4: Captured Captive

Once activated, the painting itself could be sealed away, or otherwise removed from the characters' access. Makes their fate less "certain doom" and more a process to try and find and rescue them, with a high chance of failure. Could also set it up for a reappearance down the line, even if irreversible.

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