I want to introduce an omen of an incoming demon incursion to my party that threatens the world my PCs live in. My plan is to have the party gradually trace down clues / investigate deaths and murders before finding out the truth and (hopefully) stopping it.
One "clue" I want to give to players is a magical item that materializes only when evil is approaching, However I felt just giving them the item isn't impactful or foretelling of anything. I can't verify if the players would wonder "Why did we get this weapon?" and link it to the other clues I'm handing them. Unless I wrote on it "EVIL IS COMING!!!"
My solution to this is a magical item that "follows" the party. Revealing itself as a recognizable puzzle multiple times. One that's easy to fail for the first few times but on the 4th or 5th attempt the item is given to the players. I intend on the party thinking that the item found them.
I plan the "puzzle" to appear in a variety of places across the campaign: in a sewer, a dungeon, an empty room of a manor to name a few. To tell the players that this isn't some strange dungeon specific thing, but something with more intrigue.
This, I hope at least, combined with many of the other clues (I'll hint to players of this magical item and its properties in other places) will give players enough information of the incoming incursion. But I don't want players to give up part way through and skip the item entirely because the puzzle was too difficult…
So my question is:
How do I design a puzzle where my players are intrigued enough to solve the puzzle and aren't too discouraged by failure to receive the magical item?
Footnote: 4 to 5 times is a general approximation. I feel any more or any less would make the puzzle too easy / too hard but if anyone want's to argue more or less by my guest.
Best Answer
There are a couple of common, tested solutions to this kind of problem, but first, since you discuss a "puzzle", I'll note that I've found it tricky to implement puzzles in tabletop games. I'd recommend against blocking success in the campaign behind a puzzle. Here are a few techniques I've used, including one that still includes puzzles but mitigates their potential problems. The big takeaway that they all share is that you should design your story so that it doesn't grind to a halt if the players are unexpectedly bad (or good!) at solving your challenges.
Multipart Plot Coupons
TV Tropes calls this "Gotta Catch Them All": there are a set number of items (or spells, or people) that the players have to assemble in order to gain access to the magic item. Instead of needing them to fail the first several attempts, they could find a clearly important or mysterious item in each location that you encourage them to take with them (maybe by making them seem valuable or tantalizing in some way).
In the most basic, video-gamey sense these can be four elemental crystals or the pieces of a shattered object, but I've run campaigns where the players had to find and protect the keys to magic seals that needed to stay closed, or were following the steps to a prophecy that they didn't fully understand.
Some Assembly Required
Another approach that comes to mind is to make a magic item that comes in functional parts, or evolves as you use it. The classic D&D example of this is the Rod of Seven Parts. Each piece is a useful magic item on its own and you might not realize that it is the part of a whole or how many parts there are in total. However, when you find an additional part and connect it, the artifact becomes more powerful.
An example of an evolving artifact I've used is Faarlung's Algorithm from 4e, which is a magic orb that's also a weird puzzle like an arcane Rubik's Cube. You can spend time trying to solve it (making hard Intelligence checks) in order to make it more effective. Perhaps the players can find clues or materials in their journey to enhance the item.
The key to this approach is to make the item immediately useful, even if it's not particularly strong. That way, they'll keep it with them and you can gradually bring it up to its full power.
Rivals and Conspiracies
Lastly, you can make the actual solution of the puzzle less essential to progression. Make it so that, if they solve the puzzle before you want them to get the true reward, they get a minor reward but the goalpost gets moved. Conversely, if they fail to solve the puzzle, someone else collects the reward, the players recognize it's something valuable, and they get a lead to chase it down.
This can be as simple as a rival group of adventurers or villains that's after the item for different reasons. Think of the Indiana Jones movies: the protagonist has rivals trying to get the same artifact, and there is a push and pull where they each get part of the final reward and chase each other around to get the whole thing. Your rivals could steal the item just as the puzzle is solved or, conversely, brag about solving it themselves after the players fail.
You can do this without an antagonist, too, by including a friendly character who keeps secrets. I've had great success with the classic "secret dragon" gambit, where a powerful and mysterious character has the PCs go on missions to collect things. The players slowly get suspicious until it's revealed that the character is a dragon (or some other powerful figure) in disguise. Each puzzle attempt could end in the players turning over the item or a clue to it to the benefactor, or if they failed, the benefactor could come in afterward to collect it. When the players become suspicious enough, they can confront the benefactor, and it could culminate in a fight or a friendly confession, as appropriate.