Its a new boss with 2 heads. He is found in the nether. You can spawn him with a really dark eggs.
I think this is freaky this was ment to be Mojangs secret but I MUST TELL! MUHAHAHAHHAHAHAHA!
If you like to find out this by yourself. Sleep for 1 hour wake up and before you sleep,leave a note saying Go To The Nether. This BEAST MUHAHHA can be found in the 1.4 Snapshots and 1.4.
SEE YA LATERZ LOL