This is for those submissions of small size, yet great inspirational value.
This looks like an elaborately fashioned wooden egg-cup, but it is a powerful magical tool, used mainly by witches to conjure up spirits and familiars.
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.