Two 2012 comets (Elenin and Nibiru???) Extraterrestrial Comets?

I was doing research on some nonsense about 2012 predictions, and what happened was that people were predicting that Nibiru (Planet X) and Elenin are both going to collide straight to the Earth, why are they mixing up a comet which passes this year September and the other non-existent planet on the 21st of December 2012??