Complex sentence: The plot is centered around a director of horror movies (played by Law and order actor Sam Waterston) who had directed one too many horror movies and had begun to see a Freddy Kreuger-like character whenever he looked in the mirror.
Split into simpler sentences: The plot is centered around a director of horror movies (played by "Law & Order" actor Sam Waterston). The director has directed too many horror movies and begins to see a Freddy Kreuger-like character whenever he looks in the mirror.