A bit out of the UrbanDictionary bestiary: A UDWraith is someone who (like me), hijacks another UD users name and posts things for him. It is almost impossible to tell a UDWraith post from a normal one.
Why do UDWraiths do this? Because they find it fun, or because they were burned by someone, and want to put them through some shit. Usually the former rather than the rather.
UDWraiths feed on phlogiston, which gives them live.