At the start, Nathan Fillion is dressed up as a "space cowboy". This is essentially the same outfit that he wore as Captain Malcolm Reynolds in the TV show Firefly (2002) and in the movie Serenity (2005). Molly C. Quinn continues the joke when she says "there are no cows in space" (in Firefly (2002) "Safe", Captain Reynolds transports a load of cattle to another planet), "didn't you wear that, like, five years ago" and "don't you think you should move on" (Serenity (2005) was released in 2005, or about "five years ago"). Actor Seamus Dever also dresses up as a former character - a doctor - at the Halloween party. Seamus Dever played a doctor in both General Hospital (1963) and Army Wives (2007).
When Richard emerges dressed as Malcolm Reynolds (the "space cowboy"), on one of the shelves near the lower left of his hip you can see the catalyzer Mal had to replace in Out of Gas (2002)".
While examining the first body, Castle states: "Looks like Buffy's visiting the Big Apple". Nathan Fillion played Caleb in Buffy the Vampire Slayer (1997).
Jon Huertas dresses up as character he played in Generation Kill (2008) - Sgt. Antonio 'Poke' Espera.
This was not the series stars' only roles with vampires: Nathan Fillion played uber-bad guy Caleb in the seventh season of Buffy the Vampire Slayer (1997), and Stana Katic played vampire Simone Renoir in The Librarian III: The Curse of the Judas Chalice (2008).