Buffy The Vampire Slayer (1997) - 5x11 - Triangle

Giles goes off to England to talk to the council about Glory. Meanwhile, Anya and the gang tend to the magic shop. While attempting a new spell to assist Buffy with her slaying, Willow is distracted by her and Anya's constant bickering and accidentally conjures a troll. Actually Anya turned the guy into a troll 1000 years ago when he dumped her and she was then offered the chance to become a vengeance demon. The big, dumb guy goes around smashing things with his hammer until the gang is able to stop him and send him off to troll land.