Leading up to the climax. The last witch standing is about to make her attack.
I know what's going to happen when she does -- it involves a castle and some roses -- but I have to work out the details of her appearance.
Also, whether she extends a spell that has been complicating their lives for some weeks now. It's very awkward for it to be magically impossible for them to be noticed. She meant it to be so. Their discovering a weakness will make her very unhappy.
Have her sweep in on a storm, madly cackling? Possible. No dragon, though. We've already had a dragon.