Good point - and what if there are three?
I know there are a lot of people here who aren't keen on the Old World, but this is one thing I love about it. They took a familiar setting (medieval Europe) and then (on top of the usual fantasy tropes: races, monsters, magic, etc) threw in this second, very weird Chaos moon. Two of the major holidays (Hexennacht, Geheimsnacht) and some of the months (Nachexen, Nachgeheim) are then aptly named around it. So it became far more important than just another light in the night sky.
Looking forward to what Erik comes up with here, whether that be 3 moons, or none.