A plot twist I was extremely fond of when I came up with it was this: the main antagonist of a story of mine was actually a puppet to his wife who is made prisoner to him and wishes to free herself. She has lead him into war with the mortals so that a mortal artifact that would free her would be brought to her. What's cool about it is that a bunch of characters throughout the story don't quite fit in with the antagonist and feel like seperate third parties being helpful and disadvantaging to the protagonists sporadically. You can't guess why they do it but they work for the wife. In fact, the first 'good' guy to bring up the eminent war conflict is actually a bad guy, and when you find out you think he works for the main antagonist but...!