The Mirror Universe's First Contact
"In a Mirror, Darkly" in Season 4 wasn't your standard Mirror Universe episode, since it took place entirely in that alternate world. The intro and adjusted opening theme to the two-parter did a fantastic job of making us feel like we were in that world, and were unlike anything we'd seen before. The beginning incorporates scenes from the movie Star Trek: First Contact, but wildly diverges when Zefram Cochrane greets the Vulcans not with a handshake, but a gun. The opening theme that follows is wordless and much darker, even playing over different imagery showing how the Mirror Universe's history varies from the original one we all know.