[zombie]: your question is deleted and then undeleted.
[vampire]: you only post at night (local time)
[frankenstein]: your answers are primarily made up of copy-and-pasted text from other answers.
[ghost]: your account has been inactive for 30 days or more but you continue to receive badges.
[skeleton]: your bare-bones answer consists of only a hyperlink (courtesy of Andrew the Grim)
[werewolf]: you have > 1,000 rep but get flagged as offensive/spam at least once per month.