Enderman

In a Google+ post, Notch revealed a mob called an Enderman. Endermen are depicted as a 3 meters tall, black creatures with long arms and legs. They also seem to have the ability to pick up and hold blocks. They are generally peaceful. If you look at them, they freeze, stare back at you, and become hostile. They stay frozen as long as you keep looking at them. When you look away, they will run fast towards you teleporting up to once every second to get to you faster.

Trivia

 * The name "Enderman" is derived from the internet phenomenon Slender Man, due to the mob's similar looks. Its name was given by Notch in a Reddit thread.