Speaking of the Narrator making stuff up, he’s obviously an unreliable narrator, so does that make even more of the film suspect than just the existence of Tyler Durden?
More of the movie could have just been a power fantasy on the Narrator’s behalf.
Consider the ending, where Narrator manages to defeat the alter ego he constructed, gets the girl, and watches the world burn as the Pixies play in the background. Is this on the level, or just “Jack” writing a happy ending for himself? Or did the gunshot to the head kill him, and everything after that is his dying mind?
There’s actually one strange shot toward the end of the film where we see “Jack” being dragged by an invisible Tyler Durden from the POV of a security camera. Which would be physically impossible to do, which implies that either Tyler Durden is realer than we give him credit for, or there is something else going on.