Modern development practices allow you to test “final” versions in environments identical to your live servers.

There’s an extended origin of Mewtwo that wasn’t in the theater or VHS versions which I highly recommend. It basically digs a bit deeper into what motivated Mewtwo’s creation (it has a baby Mewtwo in it!) and adds some pretty harsh tragedy to its character.

By hidden scene you mean the unavoidable and best turning point in the story, right? Cloud tells everyone on the Highwind after Tifa rescues him.