This is an idea I've had for a while about how players could communicate with an abstract entity that's influencing large numbers of people, like the tutelary spirit of a city, or something less benevolent. It's not a situation where solid rules would be useful, instead it'd rely entirely on good descriptions of the phenomenon to convey what's happening and how potentially unsettling it is.
The kind of entity I'm envisioning could be sentient or not, relatable or utterly alien, but it has to be incorporeal. There's no physical manifestation of it. No avatar or possessed medium or interpreting oracle that comes to speak directly to the players. It also has to have a subtle influence over a lot of people, on the scale of a metropolis. Possibly even a small country.
If the players want to speak to it, they just need to talk within earshot of any of its people and it will hear.
If it wants to speak to the players, it subtly directs the normal conversations of people within its domain so certain words occur in a distinct pattern or are emphasized. If you listen to the general hubbub and background noise of the city its messages are clear in the overlapping, overheard snippets of dozens of unrelated everyday conversations going on around you.
(You could easily have an antagonist who's using some flavor of mass mind control do this to talk to and taunt the players, but I prefer it as the work of a semi-scrutable intelligence.)
I'll try it out next chance I get and report back.