Originally, Xander was supposed to talk to The First in the form of Jesse (Eric Balfour), his buddy from Season 1. However, when Eric was unavailable, a replacement for him couldn't be found, so the scene was never filmed and as a result, Xander doesn't appear, making it the only time Nicholas Brendon was not featured.
Joss Whedon and Marti Noxon are both uncredited writers, each writer writing one of the four different segments. The Dawn/Joyce segment was written by Jane Espenson, the Andrew, Johnathan and Warren segment was Drew Goddard's, Marti Noxon wrote the Willow/Cassie segment, and Joss Whedon wrote Buffy's conversation with Holden.
According to the DVD commentary, a scene was intended for Kali Rocha to return as Halfrek to haunt Anya. This scene was never made as Kali Rocha was busy with her stage acting in New York.
Sarah Michelle Gellar and Alyson Hannigan are the only two actresses to appear in all 144 episodes, with the exception of the unaired pilot in which Willow was played by Riff Regan