Look, a new Minecraft mob! A secret new Minecraft mob yet to be placed in the game, but accessible by fiddling with the latest version snapshot. A secret new Minecraft mob called the Wither Boss who floats around chucking festering, withering, exploding skulls at you, your friends and your pets. Coming to a Minecraft update near you soon.
The Wither Boss is a sort of three-headed, charred skeleton, whose outer heads can launch projectiles at targets. These projectiles explode on contact, and cause a 'wither' effect that blackens your heart and leaves you tainted with its poison touch, like Marilyn Manson lyrics given mortal form. Here's the Wither Boss doing its funky thing:
I have mixed feelings about this. Helpful Reddit user SethBling has provided a world download with the Wither Boss in it, though you'll need to be running the latest Minecraft snapshot and have some idea what you're doing. I certainly don't, so will be waiting patiently for this corrupted chap to come storming into the full game.