Homecoming

In which we get an elemental struggle for survival and supremacy, the hunter becomes the hunted, Cordy becomes a slayer, and Buffy becomes a Cordy.

From the old WB Buffy website:

THE THRILL OF THE HUNT - With Cordelia flaunting her sure win in the race for Homecoming Queen, she awakens the Prom Queen from within Buffy, who tries to enlist the entire gang to help her show Cordy how it's done, but some of their allegiances may be elsewhere. Meanwhile, the blood-sucking Mr. Trick assembles a host of killers in Sunnydale for a thrilling hunt to the death to bring down the two slayers.

Cross-reference:

episodes featuring big school events:

• The Prom
  Buffy promises the gang a good time even if she has to kill every single person on the face of the earth
• Graduation Day (part 2)
  "Man, just ascend already." The class of 1999 are fully armed under their gowns...
• this episode
  Buffy fights not only an array of assassins, but also Cordelia, for the role of Queen

Cast:

• Sarah Michelle Gellar as Buffy
• Alyson Hannigan as Willow
• Nicholas Brendon as Xander
  

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• Anthony Stewart Head as Giles
• Charisma Carpenter as Cordelia
• David Boreanaz as Angel
• Seth Green as Oz
• Jason Hall as Devon
• Danny Strong as Jonathan
• Jeremy Ratchford as Lyle Gorch
• Fab Filippo as Scott Hope
• Eliza Dushku as Faith
• K Todd Freeman as Mr Trick
• Harry Groener as The Mayor
• Jack Plotnick as Deputy Mayor Finch
• Ian Abercrombie as Old Man
• Billy Maddox as Frawley
• Joseph Daube as Hans Gruenshtahler
• Jermyn Daube as Frederick Gruenshtahler
• Lee Everett as Candy Gorch
• Tori McPetrie as Michelle Blake
• Jennifer Hetrick as Ms Mason
• Chad Stehelski as Kulak