The unicorn is a mob found in the end. They look like black donkeys, have a long gray horn, and have a purple beard. If a player approachs one, it will run away at mach 2. If pumpkin pie is thrown near it, it won't run away. It can be tamed with pumpkins or pumpkin pie. When tamed, it can be ridden, but will still run from other players, unless they give it pumpkin stuff. It can be ridden up to mach .5, but can boost to mach 2 if the sprint key is held.
Eh... sounds overpowered. Not to mention impossible; Mach 2 is over 600 meters per second, if I remember correctly, and I'm reasonably sure Minecraft wouldn't be able to handle it. Being able to cross almost 40 chunks in one second seems like a bit much for something that costs only pumpkins.
No support. Unicorns could be okay, I guess? Not like this, though.
Come on. Like Sparky said, that thing runs at 600 blocks/second?! Impossible for players to capture and the game to handle. Anyways this is just a super duper CRAZY version of the vanilla horse, nothing to make it special.