When preparing an adventure

When you just know that a new threat is going to show up, and you already have a notion of what it looks like, it's a good idea to write it up before your next session. This could happen when the players tell you that they're going to do X, and you know that doing X will mean encountering Y, and Y feels like trouble. Or it could happen when you end a session on a cliffhanger (like with a missed homefront roll, or with something scary approaching) and between sessions you decide that you'll introduce a new threat.

At the end of the last session, the PCs (well, Vahid) talked about going to Three Coven Lake to find part of the Mindgem's body. I think it'd be cool to have a group of Hillfolk devoted to keeping folks away from the lakes, and to keep the horrors of the lakes contained. I name them The White Hand and write them up as a threat (an institution*).*