The party is walking through the forest at night when they come upon a clearing. Half a dozen black-robed corpses lie scattered across the ground, and a pentagram of blood is shoddily drawn in the dirt.
It seems these people summoned something they could not control. Whether or not the demon returns is up to the GM, but it would be just as rich if the demon never returned, and for the rest of the night, every stray sound or odd shadow will be jumped at!
A revolt or attack happens against a strong city/kingdom. All the losers of the battle that can be captured are brutally crucified along the roads that enter the kingdom to show their strength and as a demonstration of what happens to their enemies.