9. It's A Secret Unbreakable Sequel - Split
Jaws were dropped the world over when M. Night Shyamalan's comeback thriller Split ended with a shock cameo from Bruce Willis as his character David Dunn from Shyamalan's 2000 superhero film Unbreakable.
Above all else, it confirmed that both movies existed within the same universe, while setting the stage for a showdown between Dunn and The Horde (James McAvoy) in a prospective threequel.
It might well be the most ingeniously surprising stealth sequel mic drop in cinema history, and it's all the more impressive considering that Split premiered at Fantastic Fest almost four months before it went on general release.
Even with social media and spoiler culture being what they are these days, all but the most voracious spoiler addicts had no idea what they were walking into, in part because early festival viewers mostly seemed to honour the twist's secrecy and let audiences discover it for themselves.
Though the fruit of this reveal, Glass, ultimately proved colossally disappointing, Split did nevertheless confirm how much easier it is to keep the lid on a huge surprise when you're working with a mere $9 million budget and small crew compared to leak-prone blockbuster romps.