Air Date: 5/22/01
Buffy's third season finale, which saw the gang concluding the "High School Is Hell" allegory by literally blowing up Sunnydale High is great, but for this list we had to settle on the bleak fifth season ender, "The Gift."
For once, the eponymous vampire slayer (Sarah Michelle Gellar) does not survive a battle unscathed. The prima donna god Glory has just opened a portal to her realm, and the only way to close it is by spilling Buffy's sister Dawn's (Michelle Trachtenberg) blood. After a particularly rough season that saw her experience her boyfriend's departure, her mother's sudden death, and exhaustion from trying to keep Dawn safe, Buffy ends her pain for the world and her sister's sake by jumping into the portal herself. The Summers girls' bleed the same, and the sacrificial act effectively closes the dimensional tear, but renders Buffy lifeless too.
Thanks to network disputes, this was very nearly the end (the series jumped ship from The WB to UPN to air the final two seasons), and what a somber series finale it would've been, with a final shot displaying Buffy's headstone. The dark episode is also noteworthy for Giles' quiet, cold-blooded murder of Glory's human host. After five years of demon-fighting at great personal cost, everyone finds themselves contemplating dark choices and facing grim realities, a theme continued in the series infamously bleak sixth season.