The ghoulish creatures are three metres tall, and spend their time slowly moving blocks around the landscape. They will continue to do this until you rest your cursor on one. At that point the creature you're looking at will freeze, swivel to face you and wait for you to look away. When, inevitably, you do, it will charge, teleporting across the landscape once a second to attack you.
The Endermen are carefully designed to be a disturbing presence that haunt Minecraft's landscapes. Notch describes the design tweaks he's made to make the new mob as creepy as possible.
"I wanted this to be a mob you only saw in the distance and a mob you'd be afraid of, but when I playtested it, it mostly felt like a regular zombie. There's was a distinct mismatch between looking creepy and not actually playing creepy," he writes.
"When I made it move faster towards the player when attacking, and deal more damage, it got more difficult and I started respecting it, but it never felt creepy or scary.
"So I made it passive until you looked straight at it. And that was scary. Suddenly you could walk up to these looking beasts (they're three meters tall) and watch them as they moved their blocks around, but as soon as you happened to look straight at them, they'd attack. And by “straight at them”, I mean putting the reticle on top of them.
"You can keep them visible on screen and actually look straight at them in real life, but as soon as your in game character looks straight at them, boom."
The Endermen won't be the first enemy to play with the player's view. Left 4 Dead's Witch would remain docile until disturbed, Zelda's zombies would freeze when stared at. There's a key difference between those monsters and the Endermen. They can't teleport.
"If they're too far away to reach you in a short period of time, they will teleport about once per second. They try to make sure they always teleport to somewhere you can see, as I don't want to confuse the player as to what is happening."
With the addition of teleportation, Notch felt he'd hit the horror sweet spot he's aiming for.
"When they attack, you know it's your fault. When you happen to look at one, you can keep looking at it to figure out how to deal with it, but you know it WILL reach you very fast once you stop looking at it."
The Endermen will be added in the upcoming Adventure Update , which will make a number of major changes to make Minecraft "more like a game." Purchasers of the Humble Indie Bundle 3 can play Minecraft for free until August 14.