They are ghosts that are by the Nintendo staff. But unlike the regular Nintendo ghosts, these are very fast and hard to beat. To unlock an expert Nintendo ghost, you need to beat the regular Nintendo ghost by several seconds to unlock the expert ghost.
well to beat a world in Yoshi's Island DS you have to go level by level until you reach the final level of that world which for example, could be 1-8 (this level is a castle with a boss at the end) once you defeat the boss you move on to the next world.
You can't. However, you can unlock him on the DS version. Beat Adventure 2 mode and Wizpig will be unlocked. He is the best driver (Better than T.T.) in a car, but not so good in a Hovercraft or Plane. He shares the exact same stats with Taj.