One method of delivering campaign-spanning surprises in a game is to keep some major aspect of the setting secret from the players when the game begins, and have them discover it during play.
Some examples (N.B. there are certain games and works of fiction that could be mentioned as examples of some of the below, but doing so would be spoileriffic for those who haven't read/seen/played them, so we won't mention any by name - those of you who know them already know!):
- A modern day setting. Without further details, players would likely assume there are no supernatural elements. It can then be a surprise or shock when they discover active magic, spirits, and so on.
- A low technology setting, which the players may assume is historical or pseudo-historical. But then it is later revealed to be the leftover remnants of an advanced civilisation after some sort of apocalyptic war or other event.
- A low technology setting, which the inhabitants discover during play is actually the interior of a giant colony starship, after something went wrong and previous generations lost that knowledge.
- Any setting which the protagonists discover to be a computer simulation.
- A setting which is ostensibly some specific historical time period, but which turns out to be a recreation of that period in the present or future.
- A world which is assumed to be an alien planet, which then turns out to be Earth.
- Somewhere which seems like a normal place, until the inhabitants discover it is a giant prison from which they cannot (easily) escape.
- Somewhat similar, a place that seems normal, but is actually a giant "movie set", built to provide a setting for external viewers to be entertained by the activities of the inhabitants.
- Somewhere that seems normal, but is actually a dreamworld or psychological illusion happening in someone's imagination.
- A fantasy world with magic and monsters, which turns out to be a technological construct, with the magic simulated by technology.
- Any of the above, with robots.
Commentary by Keybounce (who has not seen the movie)
[Keybounce's comments will appear here when received.]
Commentary by memnarch (who has not seen the movie)
Definitely an odd place to store a laser sword; what if the power supply leaks or explodes! Lithium batteries are already extremely dangerous when they fail, and we actually use those. Lightsabers would need to have a much stronger power supply to work, are already shown to cut through just about anything, and that's when everything is working properly! Maybe the real reason lightsabers are so rare to find is that they level the building they're inside when the power supply fails catastrophically.
Hmmm, do Force ghosts count as undead? The people we've seen as Force ghosts all died at some point before then, so that'd likely be a yes. Or in-comic, how about brain uploading? Sure, there's no organic body or even a shape of the person they were, but I think that could count in a high tech setting if the brain was uploaded after death. Neither seem likely to take the shape of a chest though. However! We do know that mechanical beings are a thing in Star Wars. No reason there can't be a robot with an outer shell made of wood! Droids famously don't show up as life signs after all...
Rey: Okay, so I’m looking for a small chest.
GM: <roll> You spot one: Wooden, banded with iron, resting on a larger chest.
GM: There’s a hasp and staple, but no lock.
BB-8: Seems an odd place to store a laser sword.
Rey: Are there mimics in this setting?
GM: Not that you know of. But it’s a big galaxy.
Rey: I use the Force, feeling for life signs.
GM: You sense a lingering impression of conflicting emotions within the box, but it’s not alive.
Rey: Okay. Are there undead in this setting?