Robbie flamed up his hands but he saw as Tiffany multiplied herself. A second ago there was only one of her. But now there were two dozen of her. Robbie just looked around.
“You might be stronger then me,” said One Tiffany.
“But like they say there’s strength in numbers,” replied another Tiffany.
“No matter how many of us you defeat.”
“We’ll just make more and more.”
“Then it looks like I’ll have to beat you all until there’s none of you left,” said Robbie.
He began to throw fireballs at them. When each of them hit a copy it would disappear as if it had never been there. But it didn’t seem to be doing any effect since Tiffany would just make another copy.
Eventually Tiffany did an all out attack on him. She started to pile on top of him. She even multiplied even more to make herself seem heavier. Robbie was running out of options.
“You can’t beat us,” said Tiffany.
“I can give it a good try?” replied Robbie.
He then used a huge fire ball to get most of them off him. They all disappeared but Tiffany just created more

How does he win?