Pump Boy (also known as Walking Car or Mutant Car) is a yellow convertible toy car with baby doll arms instead of wheels. It is capable of walking very fast and climbing walls.
As part of the toys' rescue plan, Woody chooses Pump Boy to wind up the Frog to distract Scud. Once the toys escape outside, all the toys get into their final positions while Sid is not noticing, and Pump Boy hides in the sandbox. When the toys attack Sid, Pump Boy rallies a Charred Doll (who repeatedly utters "Mama!") and a huge, red, broken pickup truck as they emerge from the sandbox and approach Sid.