“Action Movies Feature A Hidden Villain Revealed In The Third Act”
SPOILER ALERT:
Yes, and sometimes it screws up the entire movie. Bad Times at the El Royale was a pretty good movie until it introduced a third act villain (the Mighty Thor) who was completely irrelevant to the main mystery, therefore suddenly becoming a completely different movie. Unfortunately that new movie wasn’t nearly as good as the one that got interrupted.
That’s just a plot twist. For most of those examples, it’s not like it was someone that came out of nowhere.
Well, maybe the trope is overused, nonetheless.