Jensen Ackles suffered from the flu during filming of this episode. In the last scene he had a temperature of 102.
The parking garage scene, the playing of "Ode to Joy" and being set at Christmastime are fun nods to the Bruce Willis movie Die Hard (1988). The name of the office building, Hitomi Plaza, is also reminiscent of Nakatomi Plaza, where the majority of Die Hard takes place.
The other werewolf volunteer tells Garth that a friend of his took archangel grace and became immune to silver, meaning that he can only be killed by "The full Ichabod", i.e. decapitation. This is a reference to the character of Ichabod Crane from Washington Irving's short story, The Legend of Sleepy Hollow, which famously features a headless horseman.
The film clips that show the outside of the high-rise building where Michael's base is located are actually of the fifth tallest building in Tokyo, Japan: "Roppongi Hills Mori Tower".