The role of Amanda, who first appeared in Help (2002), was originally intended as a one-time part, but was brought back as a recurring character due to Sarah Hagan's connection to writer Rebecca Kirshner, who wrote for Hagan's previous series Freaks and Geeks (1999).
Buffy tells the Potentials that her death could make one of them the next Slayer. Dawn also makes the same assumption, stating that if she were to become the Slayer, it would mean that Buffy had died. It's known that Faith became a Slayer after Kendra died, but the possibility of the line continuing due to another death of Buffy is never clear in the series, even after her death, when no new Slayer is discovered or mentioned.
Andrew makes references to Dragon Ball Z (1996), Vegeta and Goku when trying to express his desired role in the group, and also asks Dawn if she wants to "play Dragon Ball Z". James Marsters, who plays Spike, portrayed Piccolo in Dragonball Evolution (2009) and is an open fan of the anime. He would later voice Zamasu in the English Dub of Dragon Ball Super (2015).
Buffy tells the Potentials that although most people have no idea why they exist, the Potentials do - they have "a mission, a reason for being here." This is very similar to what Giles told her in Reptile Boy (1997), when he asked her how many people her age can say that they have a purpose, a commitment in life.
The twelfth episode of the season was generally the episode in which Buffy has her birthday. Apart from the first season, which was a mid-season replacement and probably began just after Buffy's sixteenth birthday, this is the only season where Buffy's birthday isn't acknowledged. In the birthday episode of the previous season, Older and Far Away (2002), Spike did suggest Buffy should not celebrate her birthday anymore.