3. Der Kindestod
Episode: Killed By Death (Season 2, Episode 11)
Der Kindestod (which translates from German as 'the child's death') was a demon who was invisible to everyone but children and those who were feverishly ill. He was a creepy looking creature (who seemed to be partially influenced in terms of appearance by Freddy Krueger) who killed children by literally sucking the life out of them. Afterwards, it appeared as though they had died of fever. Because of this, Der Kindestod preyed on children who were already ill, leaving little evidence to suspect their deaths were unnatural - especially given that no adults would ever see him carrying out the killings, due to him being invisible to them. One of his victims was a girl named Celia, whose death was witnessed by her cousin, Buffy Summers. In 1998, Buffy encountered Der Kindestod again whilst being treated for flu at Sunnydale General Hospital. After investigating the killings and discovering what was carrying them out, Buffy - having recovered from her illness - purposely contracted the flu again in order to be able to see Der Kindestod. She fought him whilst ill and weakened, but ultimately killed him by breaking his neck.