Im new here so i dont know what are the possibilities.
What about this. Every 4 hours, a random city turn into "autumn" mode.
The Rules are simple. In the automatic description will appear some random hint about the city or the MAP (heavier and funnier to me). Example: The city that was destroyed by Satan (Morroc) or East from the Circular City (Right from Geffen).
Id choose maps right after a city, to be able to everyone no matter the level or gear.
Then players will have to look for an Autumn Tree hidden on the map. (can be more) Every tree gives 1 point.
Those points goes to a general leaderboard. Can be Daily or Weekly. So at the end of the day or week, each player receive a prize depending on it own score. Can be tokens to exchange for something.
I dont know if u can decorate the map with leaves or something.