THE AMULET. Buffyverse Term/Concept/Idea/Intratext.
In "Home" (AtS 4022) a dead Lilah gives Angel an amulet and comments
That nifty, little bauble comes with the file. Apparently, it's crucial for some kind of final battle. Guess they're in short supply up Sunnydale way. A bit gauche for my taste, but, hey, not a slayer.
In "End of Days" Angel appears in Sunnydale (assisting Buffy in her slicing and dicing of Caleb) and brings her Wolfram & Hart's file and amulet. The following dialogue (from "Chosen") ensues:
BUFFY: (to Angel; re: folder) I’ll have the guys go through that, see if there’s anything new. Reliable source?
ANGEL: Not remotely.
BUFFY: Any port in an apocalypse.
ANGEL: I brought something else as well.
(He removes a silver amulet with a multi-faceted crystal at its center from his pocket.)
BUFFY: I can already tell you, I have nothing that goes with that.
ANGEL: It’s not for you.
ANGEL: I don’t know everything. It’s very powerful and probably very dangerous. It has a purifying power… cleansing power… possibly scrubbing bubbles. The translation is… anyway, it bestows strength to the right person who wears it.
BUFFY: And the right person is?
ANGEL: Someone ensouled but stronger than human. A champion. As in me.
BUFFY: Or me.
ANGEL: No. I don’t know nearly enough about this to risk you wearing it. Besides, you’ve got that real cool axe-thing going for you.
The "champion" who will wear the amulet at the final Battle of Sunnydale is, of course, Spike (he calls it his Liz Taylor accessory). The incredibly power light/energy the amulet releases eradicates the übervamps, destroying the Hellmouth and all of Sunnydale, and dusting its wearer.
In the first episode ("Conviction") of Season Five of Angel, however, the amulet mysteriously reappears back in Los Angeles at the offices of Wolfram & Hart, bringing with it a ghostly Spike, whose essence somehow survived the destruction of the Hellmouth along with the "nifty little bauble."