Whistler was originally going to be Angel's sidekick for the Angel (1999) spin-off, however, Max Perlich could not commit.
Whistler jokingly says Buffy was "prettier than the last one"; the Master said the same thing about her when first meeting in Nightmares (1997).
When Giles reveals he has an Orb of Thesulah, he mentions that he's been using it as a paperweight. This is a reference to Passion (1998), in which the magic shop owner tells Jenny that he usually sold the relics to tourists as New-Age paperweights.
Buffy and Xander's fight about whether or not Angelus should be killed for his crimes, is much like the one they'll have about Anya in Season 7's Selfless (2002), only the roles are reversed.
The Los Angeles high school exterior is the same set as the famous clock from Back to the Future (1985).