Blood Moon

The Blood Moon is a phenomenon that has baffled historians for years, it occurs on some sort of schedule but no one has been able to determine how or why they occur. The Blood Moon is when the walls between the immaterial become parchment thin and the Demons walk the land once more just like the Hendraxus's Heresy, it is encouraged that all citizens find a strong defensible location and wait out the Blood Moon as only the powerful Daemons have enough strength to remain.
Most Blood Moons give subtle warnings just before some can notice, giving a warning for those who most protect others.