Mini Boo

Mini Boos are an item in Mario Super Sluggers. These Boos make the ball invisible so the player in the outfield can't see the ball. The Mini Boos are found in Wario City and are required for King Boo to join the player's team in Challenge Mode. A fielder can still catch it if they are lucky enough. Mini Boos are similar to what a Boo spits out in Mario Power Tennis and Boolossus in Luigi's Mansion. They don't make the ball invisible for very long.