What lies under the turf deep in the earth of that grassy mound? The PCs would very much like to know...
Inspired some years ago for a Kult/CoC Halloween game
Knowledge is Power. That is, he who makes the knowledge, wields the power.
At regular intervals, a god takes control of your world's weather. Choose the gods at random each turn of the interval and begin applying their effects subtly. Their power will depend on the strength of those who worship them.
For civilised people, worship of a god actually wanes during that god's month in an effort to reduce their potential destructive effect.