Quote Originally Posted by Reinheart View Post
You have to face North when you kill the mob, make sure to move the mobs in this order before killing facing north.
Move up, up, down, down, left, right, left, right, then shout B, A!

Oh and it has to be full moon.
I heard from a friend of a friend of a friend that after doing this you also have to hit the Start button. If you're using a mouse and keyboard, you're SOL with this method.