Killer Ball is the Star Skill used by Bowser in Mario Superstar Baseball and his Star Pitch in Mario Super Sluggers.
When Bowser uses the move, the baseball turns into a Bullet Bill. If Killer Ball is used while pitching, the Bullet Bill slowly moves toward the home plate, does a loop, then zooms by the batter. If Killer Ball is used while batting, the Bullet Bill dashes across the field. If a fielder catches the ball, they are pushed a distance back.
In Mario Superstar Baseball[]
In Challenge mode, Bowser can only start using Killer Ball once the Bullet Bill item has been purchased. His son, Bowser Jr., has a Star Skill that is a variation of the Killer Ball, named the Killer Jr. Ball. It is the same as the Killer Ball except Bowser Jr.'s Bullet Bill is shown wearing his bib.