Instructions
Turn on the game. Push the "A" button on the Nintendo Wii remote. Go to the main menu. Select the time trials section. Push the "A" button again.
Choose the kind of character you wish to race. Do this by pushing the "A" button. You can also choose the kind of kart you want to use during the race. Point your Wii control to a cup that is listed on the monitor. Now move the Wii control to the course you want. Push the "A" button.
Double-click the "Ghosts" option. Select "Race This Ghost." If you not only finish your race but also beat the best time posted by the ghost, you'll unlock the specialist staff ghost.
Return to the course menu. Race one more ghost. Keep racing the ghosts until you have unlocked more than seven staff ghosts. Baby Luigi will now be unlocked.