In The Last Action Hero, Arnold Schwarzenegger's character (and his arch nemesis) 'come out' of their own action movie and experience the real world. They are eventually exposed to all of the prequels to their current film. This has a major impact on their final show down.
In Back To The Future 2, Marty and Doc go back to the the timeline which took place in the first movie. Although they did not experience the first movie in film form, they were able to watch it in person.
Although Space Balls did not have a prequel, there is a moment in that film where they watch their own movie (using an advanced technology.) By doing this, they discover major plot points, as well as experience a space time paradox by watching themselves in real time, otherwise know as 'now now'
HELMET: What the h--- am I looking at? When does this happen in the movie?
SANDURZ: Now. You're looking at now, sir. Everything that happens now, is happening now.
HELMET: What happened to then?
SANDURZ: We passed then?
SANDURZ: Just now. We're at now, now.
HELMET: Go back to then.
SANDURZ: I can't.
SANDURZ: We missed it.
SANDURZ: Just now.
HELMET: When will then be now?
HELMET: How soon?