"Or I can sit here and play with my new toys. Either way, I'm not going anywhere" Rob sounded bored but the look in his eyes was anything but. He made to attack the girls again, spurring Bill into action. It was his fault that the girls were tiny, that the magical wish granting Stone was broken, but he couldn't just stand there and let his nemesis torture them in their new defenseless size.
There was no way he could beat Rob in an actual fight, Rob was one of the strongest, toughest people Bill had ever known. And with no time or way to get to a knife or some form of weapon, Bill had only one choice; he had to use the Stone, regardless of the damage to it. He looked down to see if glowing weakly with gold-green light.
Bill closed his eyes, focused on his anger towards Rob and his desire to protect the three shrunken girls and said;
"I wish you'd pick on somebody your own size!"
Option 1: Bill's wish, much like the last one, goes awry as one of the girls turns into a massive, hulking brute that looks very similar to Rob. Almost like a female twin. Oh no...
Option 2: Rob shrinks down to three inches tall and becomes trapped in the sink. Upon inspection, Bill discovers that Rob has become a girl as well! But that doesn't make her any less mean or violent...