The Madagascar Institute built Dueling Mechanical Bulls, two mechanical bulls that compete against each other with riders in foam bull headgear. They were recently taken for a spin at the Google I|O After Hours party. Check them out in action in this video and learn more about how they were built at their website.
These two bulls require two riders (one rider on each bull, just to be clear) to function, facing each other, Mano-a-Mano, Taurus-a-Taurus. They start off slow, and the difficulty mounts, bucking and spinning faster and faster, the motion of one mirrored in the other.
images via The Madagascar Institute