For example, we could use musical instruments or actors. A list of these could be generated before the game starts, based on the number of players. Let's say there are three players (abstractly): Vasya, Masha, and Petya.
They are given a choice:
1. Al Pacino
2. Robert De Niro
3. Jeff Bridges
The players choose any available option from the list, and a hint is created for a specific quest (thankfully, there's plenty of information and facts in the wiki, and not just there – like the example with the magic violin in the neighboring thread).
But even just using the wiki, you can hide a lot of information!
It could be anything: actors, directors, military leaders, tarot decks, countries... basically anything that has information available.
For example, Vasya chooses Jeff Bridges,
Masha chooses Pacino,
and Petya chooses De Niro.
Then Vasya kills someone, and the game master creates a hint based on Jeff Bridges.
For example, the victim was found at night in a movie theater where a film about a high-ranking government official on vacation was playing.
I'm just giving an example, and it's the first thing that came to mind.
The solution: "at night in a movie theater" – a reference to the film "The Last Picture Show," Jeff's first role. "A high-ranking government official on vacation" – a reference to Jeff's role in the film "The Fisher King."
So, instead of actors, it could be anything, but from the same general category.