The was originally conceived of as a self-contained episode called "Hell".
The spell Tara uses to find Willow and Xander in the woods, is the same spell Willow unsuccessfully tried to perform in S4's Halloween episode "Fear, Itself."
Xander says: "Yeah, we got trouble. Right here in Hellmouth City". This is a reference to the song "Ya Got Trouble", from the musical The Music Man (1957).
Xander says: "The better to cut you down to size, Grandma". This is a reference to the dialogue between the girl and the wolf in the tale "Little Red Riding Hood" (1697, 1812).