My favorite take on this:

Humor, jokes, memes about TTRPGs
My favorite take on this:

That last question is ambiguous enough (in this specific scenario) that either answer would work. It's both true that the other guard can't tell her something happened (due to being dead), while the other guard would have said that something did happen if he had been able to. So it's a meaningless question but the wife doesn't know that since she doesn't know the guard is dead.
Which just adds another layer to the joke lol.
Alternate solution:

Is there an actual plot to Mimi, or is she just a complete chaos goblin?
Simply goblin
I'm not going to trust the rules given to me by a guard who might be the one who lies
I got an unexpected laugh from Rick and Mortys take on this. His answer was "you ever fuck this guys wife?" And watched them fight to the death.
Ah man, I miss Rick and Morty before you know... everything.
I mean, the Barbarian asked the one question and didn't gain anything from it. Knowing which one is the liar doesn't... help anymore.
Ah. Normally I see this with no limit on questions. You're right. It'd only work with at least two questions.
I've only heard it with one question, that's the whole point. Otherwise you just ask a guard some trivial question (e.g. What color is the sky?) to determine which is the liar, then just ask which is the safe door.
The whole point is to get the information you need from a single question.
Maybe I've only seen a fucked up version.
That's why it's funny.
That assumes the other guy holds to his principles in the face of death. If I were the dm, the act of tearing the other guy's head off and then threatening to do the same to the other one unless granted another question would at least grant advantage on an intimidation check
Ask either guard: "If I asked the other guard which door led to the castle, what would they say?" The answer is always the door that leads to instant death; enter the other door.
Then, rip both of them in half and knock down the safe door so that everyone after you immediately knows the safe route
If you rip them both in half, then two of your party are cursed to be the next two truth/lie guards. Roll for unintended consequences.
“So, you’re telling me I could have just greater restoration’d the guards rather than killing them? My god isn’t going to like this.”
The guard replies "I don't know for sure".
This puzzle is always presented as difficult, but why not just ask a known? If your eyes are brown just ask “Are my eyes brown?” You’d immediately know which one lies or tells the truth.
E: I missed the limit of one question.
The difficulty comes from only being able to ask one question. It's very easy to figure out the liar, but it's much more difficult to figure out the liar and the correct door in the same question
Because there are two doors and only one question. If you ask a known question unrelated to the door you find out who the liar is but lose your opportunity to ask them which is the correct door.
Knowing who lies and who tells the truth doesn't tell you which door leads to the prize and which to death.
But they gained no information on which door to choose ='(
Barb could simply kill Death-itself if choice was certain death room.
Opening the certain death door reveals a guy in a dark robe with a scythe: "Hey, what's up?"
The Barbarian got what they wanted, which is to have an excuse to rip another head off.
For years, I had my own headcanon for the Labyrinth movie. In the scene, the young Sarah correctly solves the riddle, passes through the correct door, says "This is a piece of cake!" and then she immediately falls down a pit of doom. This confused me, because she got the answer right. So I reasoned that the guards were both liars, and because they both participated in explaining the rules, they were lying about the rules.
It was only a few years ago that I read in an interview that the Labyrinth (or Jareth) dropped her down the hole because she said it was a piece of cake. It was her arrogance that set her back, not that she got the riddle wrong.
But now it still bothers me that the liar, whichever one he is, helps explain the rules of the scenario. If he always lies, then she can't trust that either of them ever tells the truth. The rules have to be described separately, like on a sign or by a disinterested third party. Or you could phrase it differently, like "One of us will answer your question truthfully, and one of us will answer your question dishonestly." That way you avoid saying that they always lie, and specify that the lie will only be in response to the one question.
Fuck, I've had too much coffee. How the fuck did I get up on this soapbox? Why are you still reading? Go do something productive.
Go do something productive.
No.
This still doesn't accomplish the goal of knowing which door will kill you. All you've done is determine which guard is the liar.
I believe that's the joke. The barbarians intelligence isn't usually very high.
I love playing low Intelligence high Wisdom characters. Because Wisdom governs stats like Perception, Insight, and Animal Handling. So your character will notice things that the rest of the party misses, but often doesn’t have the intelligence to put the individual pieces together.
Once played a high wisdom barbarian. He would notice things like traps or clues, but I would RP it with things like “Hey, why’s that wire stretched across the path? Someone is going to trip over that…” The other players very quickly learned to pay attention whenever I asked stupid questions, because it was usually my way of announcing “I noticed something that the rest of you missed.”
So you ask them which way leads to the castle and you don't pick the way they say.
If we're assuming that these things are actually bound by some kind of rule stating they literally cannot lie or literally cannot tell the truth.
But you asked your one question to the one remaining guard. You gained no intel.
The first time I encountered a version of this riddle it actually wasn't Labyrinth. It was an old black and white episode of Dr Who aired on PBS when I was a little kid. Same scenario but if I recall, robots instead of guardsmen. I think the good doctor solved the riddle in the typical way of asking one robot what the other would say. I'm looking for it now but I can't find the scene.
So the traditional answer here is to ask them to point at the door the other guard will say is safe.
However, I'm curious, does anyone know of any other valid solutions?
"Is the guard that tells the truth standing in front of the safe door?" If they say yes, you go through their door, if they say no then you go to the other one