This might get spoilery (especially in the comments section), so consider yourself warned.
I have a friend who argues that Rob Zombie's Halloween 2 is really about Laurie Strode as the killer Michael Myers -- that Myers only exists in the sequel as part of her fractured imagination, and that she's the one doing the killing. It's an interesting spin, I guess, but I'm loathe to revisit the abysmal movie to find out if Zombie really did set up the film in that way. It certainly brings to mind the French slasher Haute Tension, a movie that becomes almost a completely different movie once it crosses the finish line and turns everything you've just seen completely upside-down.
There are two basic varieties of mind-benders -- the twist ending, with a finale that colors everything that's taken place before the twist in a different light (like Haute Tension and The Sixth Sense) or the open-to-interpretation mind-bender (like Halloween 2 or Total Recall), in which the events of the film could legitimately be viewed two entirely different ways. Some films, like Memento and Irreversible, actually have twist beginnings, actions at the start of the film that don't make narrative sense until things unspool backwards for us, and sometimes even then require a second viewing to become clear.