In keeping with this season's theme of going "back to the beginning", in the shot right before the opening credits Buffy greets Rona by saying "Welcome to the Hellmouth", which is the title of the first show of the series.
Xander is shown sleeping on the couch at Buffy's house, completing the Scooby Gang's migration to the Summers residence.
When Andrew says he's bored, "Episode One bored," he's referring to 'Star Wars: The Phantom Menace" (1999), considered by most Star Wars fans, of which Andrew is one, to be the worst entry in the series.
Andrew mentions the Justice League putting "their differences aside to stop the Imperium and his shape-shifting alien horde". This is a reference to the Justice League debut triple-part episode "Secret Origins," which aired on November 17, 2001.
Buffy: "So I'm here to tell you, you try anything, try to run... you ever see the movie Misery?". Andrew: "Six times. But the book was scarier than the movie because instead of crushing his foot with a sledgehammer, Kathy Bates chops it off with..." (realising) "I'll be good". This is all true, in Stephen Kings original 1987 novel, Misery, the character Annie Wilkes chops off Paul's foot with an axe. In the 1990 movie adaption, she breaks Paul's ankles with a sledgehammer. The change was to reduce the level of gore in the movie.