Buffy the Vampire Slayer/Recap/S2 E8 The Dark Age

A corpse-possessing demon comes to Sunnydale with a personal vendetta against Giles, revealing facts about his Dark and Troubled Past.

Tropes
"Miss Calendar: All right guys, the first thing we're gonna do is-- [Buffy enters] Buffy!
 * A Day in the Limelight: For Giles
 * Almost Kiss: Averted; the school bell rings as Jenny and Giles are about to kiss, but they do it anyway.
 * Body Surf
 * Bookshelf Dominoes: Ethan tries to knock down Buffy this way.
 * Brain Bleach: The Scoobies have this reaction at the thought of Giles and Jenny having sex.
 * Conveniently Placed Sharp Thing: Ethan Rayne has Buffy tied up, with her arms wrapped around the edges of a table and tied together beneath it. There is a conveniently located screw sticking out the bottom of the table that she uses to saw through the ropes.
 * Cower Power: Rayne leaps behind Buffy when Zombie!Philip does his Super Window Jump.
 * Cut Phone Lines
 * Dark and Troubled Past / Former Teen Rebel: Giles
 * Demonic Possession
 * Drowning My Sorrows: Giles again
 * Evil Sounds Deep / Kubrick Stare / Animal Eyes: Possessed!Jenny.
 * Fantastic Aesop: Demonic possession = drug experimentation.
 * Finger-Twitching Revival: Jenny
 * Foe Yay: Apart from the usual Giles/Rayne, Eyghon throws in plenty of Double Entendre while fighting with Giles.
 * Getting Crap Past the Radar:

Xander: Huh? Did I fall asleep already?"

"Buffy: I'm gonna kill you. Will that blow the whole karma thing?"
 * The Glasses Come Off
 * Glowing Eyes of Doom
 * Gotta Kill Them All: Eyghon's motivation
 * Groin Attack: Cordelia shows she is good in a fight after all.
 * Hilarious in Hindsight: At the beginning of the episode Buffy is training away, in gym clothes. Now take a look at Kim Possible, which in many ways is Buffy with a spy rather than horror theme. Her casual outfit of lime top and blue cargoes is a carbon copy of Buffy's gym clothes.
 * Hollywood Homely: Cordelia telling Xander that he needed "a year supply of acne cream".
 * I'll Kill You!

"Willow: Willow: HEY! We don't have time for this! Our friends are in trouble! Now, we have to put our heads together and, and get them out of it! And if you two aren't with me a hundred and ten percent, then get the hell out of my library!"
 * Kill It with Fire: Ethan burns off his tattoo with acid.
 * The Main Characters Do Everything: Angel defeats Eyghon
 * Mark of the Beast / Embarrassing Tattoo: The Mark of Eyghon
 * My God, What Have I Done?
 * No Ontological Inertia: The demon Eyghon possesses Jenny, whose appearance gradually becomes demonic. When Eyghon is expelled, she immediately reverts.
 * Not So Different: Knowing Giles was also foolish in his younger years increases Buffy's bond with him.
 * Our Zombies Are Different
 * Out-of-Character Moment: Willow turns into The Determinator when Xander and Cordelia are about to fight.

"Ethan: Now this may sting a little, just at first. But don't worry, that'll go away once the searing pain kicks in."
 * Foreshadowing Willow's leadership role whenever Buffy and Giles are not around, particularly in early Season 6.
 * Revealing Hug
 * Sinister Silhouettes: Eyghon before he enters Rayne's shop.
 * Unspoken Plan Guarantee: Willow's plan for defeating Eyghon.
 * Villain Exit Stage Left: Rayne, naturally.
 * You Won't Feel a Thing: Subverted.