A mob from the night stays through they day, does not move, and can only be attacked once.

Basically, there was a Skeleton stuck on the surface, not burning during the daytime. At first, I thought that he would need to be updated like blocks so I hit him one time. He DID take damage, however he did not die nor was I able to hit him further. He also took up space, he wasn't just the model of the Skeleton without a hitbox. Saving and quitting to title then reloading fixed this bug, it seems. Nothing game breaking, but just a tad annoying.

Here is a picture of the Skeleton: http://i.imgur.com/uJy4jjl.jpg