Will someone please explain this riddle solution to me?

WARNING: If you are prone to migraines, perhaps you should not read the details.

This Q comes from the “Puzzle of The Two Doors” in the movie, LABYRINTH, and admittedly, SOME of these details come from other online chats regarding the puzzle, but here is what I have been able to find:

The heroine comes to a pair of doors, each guarded by a muppet. One of the guards tells her that one door leads to the center of the Labyrinth and the other leads to (dun dun DUN!) certain death! The heroine is told that the guards can point her to the right door, but one guard always tells the truth and the other always lies.

She works out the standard solution to the puzzle (ask one what the other would tell her, then do the opposite) and proceeds.

But, she gets the rules of the riddle from one of the guards, and he might just be the one who always lies!

So what kind of variations would that imply? Obviously, they can’t both be telling the truth (since the statement that one lies would then be a lie). The statement “one always tells the truth and one always lies” is still a lie if both guards lie. So you’ve either got one liar + one honest or two liars.

How could a smart player/character figure out what’s really going on so they can avoid (dun dun DUN!) certain death? Obviously, there needs to be some rules. Let’s say:

The guards are only forced to lie/be truthful when talking about the challenge itself.

What clues would be needed to indicate that this isn’t the “standard” scenario?

Players who just assume that the rules match the expected riddle might get ticked off if they turn out to have gone through the wrong door. Playing against player assumptions shouldn’t edge into playing against the players.

Usually, this type of challenge has a limit on the number of questions you can ask. How many questions would be needed to determine (1)how many liars (1 or 2) and then (2) which door (using the information from 1 to determine how to ask the question)? Or is there some convoluted combination of “what would he say you would say he would say is the right door” that collapses down to a known state regardless of one or two liars?

Or is there just too big a chance that this would go horribly wrong? I doubt consequences would be as high-stakes as “instant death vs. progress” (although “easy route” and “hard route” are definite possibilities).

Don’t hesitate at all to “talk down to me,” when explaining this, because I really have tried to understand it (and all of the purported “solutions,”) and I believe I am going to start drinking again, after 37 years of sobriety.