There have been many antagonists that have appeared in Buffy the Vampire Slayer. Be it The Master, Angelus, Spike, Glory, the Trio or The First Evil, Buffy is a show which knows how to make a great bad guy (excluding maybe Adam). But amongst the Big Bads and the Little Bads - Mr Trick, Caleb, Drusilla, and Darla - there also a great number of villains that appear in only one episode of the show.
Commonly referred to as the "Monster of the Week", these bad guys are fleeting, but many leave a mark.
Silent demons, fear demons, vampires, ghosts and more, Buffy, over 144 episodes, has got a great number of brief antagonists. Some have failed ("Doublemeat Palace" was a weak one; so was the demon in "Shadow"), but others were fully realised and in many cases underused.
The following list will focus on these one time bad guys. Be it for fear factor, appearance, importance to the arc of other characters or sheer entertainment value, all the entries are well deserving of their place and all pack a punch.