10The Replicator (S8E24)
The main villain of the eighth season of Criminal Minds was none other than Mark Hamill who portrayed John Curtis, also known as The Replicator. He was an interesting villain since he was a former FBI special agent with a genius-level IQ who turned into a serial killer. In season
8, he started to create copycat crimes of cases the BAU solved in the past.
There have been few deaths of the main Criminal Minds characters, but that changed in the episode "The Replicator" when Curtis killed BAU Section Chief Erin Strauss as revenge when he was left to take the blame on an older case. This season finale featured a huge loss, a great climactic scene, and it was a perfect goodbye for the season.